Preparation, Characterization, and Testing of a Carbon-Supported

Article pubs.acs.org/IECR

Preparation, Characterization, and Testing of a Carbon-Supported Catalyst Obtained by Slow Pyrolysis of Nickel Salt Impregnated Vegetal Material Laurenţiu Ceatră,† Oana Cristina Pârvulescu,*,† Inmaculada Rodríguez Ramos,‡ and Tănase Dobre† †

Chemical and Biochemical Engineering Department, University POLITEHNICA of Bucharest, 1-3 Gheorghe Polizu, 011061, Bucharest, Romania ‡ Group for Molecular Design of Heterogeneous Catalysts, Institute of Catalysis and Petrochemistry, Marie Curie 2, Cantoblanco, 28049 Madrid, Spain S Supporting Information *

ABSTRACT: A new method for synthesis of carbon-supported catalysts where precursors were obtained by slow pyrolysis of whole (8 mm) and ground (4 and 2 mm) corn grains impregnated with nickel nitrate solution is described. Carbon-supported nickel catalysts prepared by precursor activation at three levels of maximum activation temperature (600, 680, and 750 °C) were characterized and tested in the liquid-phase cinnamaldehyde hydrogenation. The influence of corn grain size and maximum activation temperature on catalyst texture, nickel loading, nickel nanoparticle size, and hydrogenation reaction performances was evaluated. An increase in BET specific surface (92−379 m2/g), porosity (0.13−0.60), mean pore diameter (12.8−22 nm), nickel loading (3.56−25.41%), and nickel nanoparticle size (21−55 nm) was found with decreasing grain size and increasing activation temperature. The highest values of cinnamaldehyde conversion (97%) and initial turnover frequency (0.31 and 0.36 s−1) were obtained for supported catalysts prepared from ground grains activated at 750 °C.

■

exchange.2,32−34 The thermal treatment stage commonly includes drying, calcination, and activation by reducing.1,2,35 Typically, the supported metal salt is converted to a metal oxide by calcination, and this oxide can be further reduced to a metallic state by a reducing agent, usually H2 or H2−N2/Ar mixture.2,35 Catalyst activation by reducing is performed by the manufacturer or/and by the user prior to the start of the catalytic experiment (prereduction/reactivation). The thermal treatment significantly influences the porous structure of supported catalyst and the size of metal nanoparticles.1,11,35 A special thermal treatment consists of precursor pyrolysis, e.g., pyrolysis of ionic resin wherein an active metal has been dispersed by ion exchange.2,32−34 The activity and selectivity of a supported monometallic catalyst depend on electronic structure, loading, and particle size of the metal, support type and its textural parameters (specific surface area, pore size distribution, pore volume), preparation method, as well as reaction conditions (prereduction/reactivation time, temperature, pressure, initial reactants concentration, reactor type, and reactant and product structure).36,37 Because almost all physical−chemical properties of a supported catalyst are influenced by the synthesis method, a control over its preparation is necessary in order to improve the catalytic performances. There are more industrial applications and scientific research based on supported metal catalysts, e.g., hydrocarbons

INTRODUCTION A supported catalyst generally consists of a catalytically active component, a support, and optionally, one or more promoters. The use of a support mainly aims at obtaining a high dispersion of active component, usually a nanosized metal, in order to maximize the catalytic surface.1 For this, the support should have a large surface area as well as suitable pore size distribution and chemical properties. Acidic (Al2O3, SiO2) and basic (MgO) oxides, zeolites, clays, and carbons are the most common supports.1−3 Having multiple advantages, i.e., well-developed porosity, high specific surface area, stability in both acidic and basic media, resistance at high temperature in an inert atmosphere, the possibility of tailoring the pore size distribution and surface chemical nature, and easy metal recovery from the spent catalyst, carbon materials such as activated carbon,4−13 nanotubes,10,14,15 and nanofibers16−19 have been widely employed in heterogeneous catalysis. Among them, the activated carbon is the most used support, especially due to its great accessibility and economical preparation from various natural carbonaceous precursors, e.g., coal, wood, and also agricultural or forest byproducts.2,3,20−24 There is a wide range of methods applied in laboratory and industry for the manufacture of supported catalysts. A preparation method for supported monometallic catalysts generally involves two stages. A supported catalyst precursor is obtained by metal salt dispersion onto a support in the first stage, whereas the supported catalyst is synthesized by a precursor thermal treatment in the second stage. Metal dispersion onto a support can be achieved by various techniques, e.g., impregnation,2,4,6−15,17,19,25−28 deposition− precipitation,2,5,16,18,19 coprecipitation,2,29 sol−gel,30,31 and ion © 2016 American Chemical Society

Received: Revised: Accepted: Published: 1491

October 28, 2015 January 20, 2016 January 25, 2016 January 25, 2016 DOI: 10.1021/acs.iecr.5b04059 Ind. Eng. Chem. Res. 2016, 55, 1491−1502

Article

Industrial & Engineering Chemistry Research reformation,7,26 Fischer−Tropsch synthesis,28 alcohols carbonylation,9,13 chlorinated benzene hydrodeclorination,4,12 hydrogenation of unsaturated molecules such as aromatic rings,11,17,19,29 aliphatic olefins,10,32 and unsaturated aldehydes and ketones.1,5,8,14,15,18,25,27,36,37 Selective hydrogenation of cinnamaldehyde (CAL) yielding either cinnamyl alcohol (COL) or hydrocinnamaldehyde (HCAL) as the main products is an important reaction from practical and fundamental points of view. Both products have multiple applications in the fine chemicals industry; i.e., COL is employed in the production of perfumes, photopolymers, inks for multicolor printing, animal repellents, and intermediates in organic synthesis, whereas HCAL is used in the preparation of perfumes, sunscreens, and herbicides as well as in the synthesis of cinnamic acid, a precursor of various pharmaceuticals.38 Referring to the theoretical aspects, the catalytic hydrogenation of CAL is a model reaction to study the influence of process parameters on the catalytic activity, usually expressed in terms of CAL conversion and/or turnover frequency, and product selectivity.1,5,17 The selection of suitable active metal, support, preparation method, and operation conditions in order to obtain optimum process performances is a challenging task in the liquid-phase CAL hydrogenation. Electronic structure and particle size of the metal affect the mode of CAL adsorption onto the metal surface and consequently the selectivity to a semihydrogenated product.1 As CAL adsorption occurs perpendicular (top-on), the hydrogenation of the CO bond producing unsaturated alcohol (COL) is enhanced, while as it is parallel (flat), the hydrogenation of the CC bond generating saturated aldehyde (HCAL) is promoted.1,36,37 In the monometallic catalysts which are commonly applied, the metals are selected from the transition-metal groups 8−10, i.e., Ru (group 8), Rh and Ir (group 9), and Ni, Pd, and Pt (group 10), having six, seven, and eight electrons in the incomplete d subshell, as follows: 4d6, 4d7, 5d7, 3d8, 4d8, and 5d8, respectively.1 It was assessed that the larger the d-band, the stronger the repulsive interaction between metal and CC bond and the higher the probability of CAL molecule top-on adsorption, promoting the hydrogenation of CO bond.1,5,36 The d-band width increases in the order Ni < Pd < Rh < Ru < Pt < Ir; consequently, Ru, Pt, and Ir exhibit a strong repulsive interaction with CC bond and a high selectivity to COL, whereas Ni, Pd, and Rh favor the synthesis of HCAL due to their low repulsive effect.1,5,8,36,37,39 A beneficial influence on the selectivity to COL due to a steric effect of phenyl group from the CAL molecule was reported for a size of metal nanoparticle larger than 2−3 nm.1,8,25,37 Accordingly, a steric repulsion appears between the nanoparticle surface and phenyl group, promoting the top-on adsorption of CAL molecules and the hydrogenation of the CO bond.8,25,37 Typically, the larger metal nanoparticle size, the higher the selectivity to COL.8,37 Operation conditions have a significant effect on catalytic performances. CAL conversion rate usually increases with the temperature, whereas a high initial CAL concentration can conduce to the top-on adsorption of CAL molecules and hydrogenation of CO bond, leading to a large selectivity to COL.1,14,18,27,36 Liquid-phase CAL hydrogenation is commonly conducted in batch reactors under the following conditions: 50−130 °C temperature, 0.1−5 MPa hydrogen pressure, 500− 1600 rpm stirring rate, 0.01−0.42 mol/L initial CAL molar concentration, 35−2000 initial CAL/metal molar ratio, and

using ethanol, 2-propanol, or cyclohexane as solvent.1,5,8,14,15,18,25,27,36,37 This paper reports the preparation, characterization, and evaluation of monometallic-supported catalysts based on nickel as catalytically active metal and corn grains as support. Precursors were obtained by support impregnation with nickel nitrate solution, and these precursors were further pyrolyzed under carbon dioxide flow. The nickel nitrate was converted during the pyrolysis according to the following reactions: (i) decomposition into nickel oxide, nitrogen dioxide, and oxygen: Ni(NO3)2 → NiO + 2NO2 + 1/2O2; (ii) reduction of nickel oxide: NiO + H2 → Ni + H2O, NiO + CO → Ni + CO2, NiO + C → Ni + CO; (iii) reduction of nitrogen dioxide: 2NO2 + 4CO → N2 + 4CO2, 2NO2 + 4H2 → N2 + 4H2O, 2NO2 + 2C → N2 + 2CO2.40−43 Carbon-supported nickel catalyst as well as pyrolytic oil and gases were obtained as pyrolysis products. Carbon-supported catalysts prepared under various experimental conditions were characterized by nitrogen adsorption and desorption at 77 K, atomic absorption spectroscopy (AAS), Xray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric (TG) and differential thermogravimetric (DTG) analysis. Further, their performances in the liquid phase CAL hydrogenation were tested. Especially in the regions where the corn crops are abundant, the grains may be used not only as staple food and livestock feed but also as raw material for industry. In this context, slow pyrolysis of metal-impregnated corn grains could be a promising alternative to treatment by calcination and reduction, which is commonly applied to synthesize carbon-supported catalysts. From one side, unlike lignocellulosic wastes, which are widely used as feedstock, corn grains provide the opportunity to prepare granular supported catalysts with relatively uniform size, shape, and structure. From the other side, the pyrolytic oil and gases can be further upgraded to obtain fuels and chemicals, improving the process efficiency.

■

EXPERIMENTAL SECTION Preparation of Fresh Precursor. A supported catalyst precursor was obtained by impregnation of a carbon support with an aqueous solution of metallic salt. Whole and ground corn grains with an equivalent spherical diameter, dG, of 8, 4, and 2 mm were employed as carbon support. The metallic salt used for grain impregnation was nickel(II) nitrate hexahydrate, Ni(NO3)2·6H2O, purchased from Sigma-Aldrich. Batch impregnation was performed at 25 °C for 72 h at a nickel nitrate concentration of 300 g/L and a solid/liquid ratio of 1/5. Nickel-impregnated corn grains were further filtered and dried in an oven at 105 °C for 72 h. This dry impregnated vegetal material, keeping the shape and dimension of unimpregnated material, is called fresh precursor (P). Preparation of Pyrolytic Precursor. A thermal treatment of fresh precursor by slow pyrolysis was performed. The pyrolysis was conducted from ambient temperature to about 350 °C in the presence of carbon dioxide as carrier gas and reactant. The laboratory setup used for pyrolytic process study was described in our previous studies.41−44 A 400 g sample of fresh precursor was packed in a 50 mm diameter and 500 mm height quartz column. The column wall was heated by an electrical resistance supplying a heating flux of 2600 W/m2. The carbon dioxide up-flowed through the material fixed bed and left the column along with the volatiles produced during the pyrolysis. The precursor mass, column wall temperature, and bed center temperature were continuously monitored. Values 1492

DOI: 10.1021/acs.iecr.5b04059 Ind. Eng. Chem. Res. 2016, 55, 1491−1502

Article

Industrial & Engineering Chemistry Research lower than 10 m2/g were obtained by analysis of BET surface area of the char resulted by fresh precursor pyrolysis; therefore, it was further activated in order to obtain a carbon-supported catalyst with a highly developed porosity. This pyrolytic char, keeping the shape and dimension of fresh precursor, is called pyrolytic precursor (PP). Characteristic data of fresh precursor pyrolysis under carbon dioxide flow are summarized in Table S1. Preparation of Carbon-Supported Nickel Catalyst. A carbon-supported nickel catalyst (CC) was prepared by activation of pyrolytic precursor in order to increase its specific surface area. The activation was performed by slow pyrolysis under carbon dioxide flow in a MK2-M5 CI Electronics microbalance. The thermobalance was equipped with a furnace, a system for gas flow measurement and control, a system for furnace temperature measurement and control, as well as a data acquisition system. A 0.2 g sample of pyrolytic precursor, which was ground at a mean particle diameter of 0.33 mm, was loaded in the furnace, heated from the ambient temperature to a maximum activation temperature, tmax (600, 680, and 750 °C), and then kept for 1 h at this activation temperature. The sample mass and operation temperature were continuously monitored. Characteristic data of pyrolytic precursor activation under carbon dioxide flow are summarized in Table S2. Characterization of Corn Feedstock. Proximate analysis of corn grain was performed according to specific procedures and equipment for cereals.45−48 Moisture, starch, and protein percentages were determined by an OmegAnalyzer G (Bruins Instruments USA), whereas those of ash and fat were evaluated according to the procedures of AOAC method nos. 923.03 and 922.06, respectively. A PerkinElmer 2400 Series II CHNS/O Elemental Analyzer was used for ultimate (elemental) analysis. Characterization of Precursor Thermal Behavior during the Pyrolysis. TG and DTG analysis was performed to study the thermal behavior of fresh and pyrolytic precursors during the pyrolysis process. Characteristic curves were plotted based on results obtained in the pyrolysis equipment, according to the operation parameters given in Tables S1 and S2. Characterization of Porous Structure. Specific surface area, porosity, pore size distribution, and mean pore diameter of pyrolytic precursor and carbon-supported nickel catalyst were evaluated based on nitrogen adsorption and desorption isotherms at 77 K, i.e., adsorbed/desorbed liquid nitrogen volume, V, vs relative pressure, P/P0, obtained in an ASAP 2420 surface area and porosity analyzer. The samples were degassed at 180 °C for 16 h prior to analysis. Specific surface area was estimated using BET equation for the first part of adsorption branch (0.04 < P/P0 < 0.20), porosity was calculated depending on the value of V at P/P0 = 0.99, whereas pore size distribution and mean pore diameter were determined applying BJH method to the desorption branch. Determination of Nickel Loading. Nickel loading of pyrolytic precursor and carbon-supported nickel catalyst was determined by AAS analysis, using a Thermo Elemental Solaar M5 atomic absorption spectrophotometer equipped with a graphite furnace and flame atomization. Prior to test, the samples were mineralized in an aqueous solution of nitric acid at a concentration of 65% for 24 h and then filtrated and diluted. Characterization of Nickel Crystallites and Particles. The presence of nickel crystallites was confirmed by XRD experiments conducted on a Bruker-AXS D8 ADVANCE X-ray diffractometer for pyrolytic precursor and an Xpert Pro X-ray

Diffractometer for carbon-supported catalyst. Both devices have used Cu Kα radiation, operation voltage of 45 kV, and current of 40 mA. Nickel crystallite size was calculated by Scherrer formula 1, where dNi(c) (nm) is the equivalent spherical diameter of crystallite, K the shape factor (K = 0.9), λ the X-ray wavelength (λ = 0.15406 nm), β (rad) the peak full width at half-maximum corrected for instrumental broadening, and θ (rad) the Bragg diffraction angle. dNi(c) =

Kλ β cos θ

(1)

TEM measurements were performed for carbon-supported nickel catalyst using a JEOL-2100F transmission electron microscope. Histograms of nickel particle size distribution were obtained from TEM analysis based on measurements of about 200 randomly selected particles from at least 30 images of each sample. Testing of Carbon-Supported Nickel Catalyst. Carbonsupported nickel catalyst performances were tested in the liquid phase CAL hydrogenation. The process was conducted in a stainless steel autoclave equipped with a glass vessel, an electrical resistance, a mechanical stirrer, a pressure gauge, a thermocouple, a sample port, a gas inlet, and an outlet. Prior to the reaction, the supported catalyst was reactivated under hydrogen flow in a sealed glass reactor placed in a furnace according to the following steps: (i) heating from the room temperature up to 400 °C at a heating rate of 3.2 °C/min, (ii) reduction at 400 °C for 2 h, and (iii) cooling from 400 °C to room temperature. After the reactivation stage, a mixture containing 0.10 L of 2propanol, 0.40 g of CAL ([CAL]0 = 0.03 mol/L), and 0.018− 0.126 g of carbon-supported catalyst (R = [CAL]0/[Ni] = 40) was fed in the autoclave, and the system was sealed. The autoclave was flushed three times with 0.5 MPa helium in order to remove any traces of air, and then the system was charged and recharged three times with hydrogen until the helium was completely removed. Afterward, 3 MPa of hydrogen was introduced, the liquid phase temperature was raised to 60 °C, and the reaction was initiated by a vigorous stirring (1000 rpm) of reaction mixture. Samples were withdrawn at different intervals, filtrated, and analyzed on a Varian 3800 gas chromatograph equipped with a FID detector and a capillary column. Compounds concentrations were identified by comparison with an internal standard (anisole).

■

RESULTS AND DISCUSSION Characterization of Corn Feedstock. Data on proximate and ultimate analysis of corn grain are given in Table S3. Tabulated results highlight a carbonaceous (44.7 wt % C) material with high starch content (62.2 wt %) and low percentages of ash (1.2 wt %) and fat (3.8 wt %). Corn grain contains also 8.7 wt % proteins as well as 11.2 wt % fibers and other saccharides. These data are in a good agreement with other findings, e.g., 62.5 wt % starch, 1.2 wt % ash, 3.7 wt % fat, 8.3 wt % proteins, 8.3 wt % fibers (cellulose, hemicellulose, and lignin), and 3.1 wt % other saccharides.48 Low percentages of N (1.2 wt %) and S (0.1 wt %) indicate low emissions of nitrogen and sulfur oxides during the pyrolysis. Characterization of Fresh Precursor Thermal Behavior during the Pyrolysis. TG and DTG curves registered for fresh precursor pyrolysis from the ambient temperature to about 350 °C under carbon dioxide flow, i.e., material mass 1493


Article

Industrial & Engineering Chemistry Research

Figure 1. Characteristic TG (a) and DTG (b) curves of fresh precursor pyrolysis: ◆, P1; ■, P2;

▲,

P3.

Figure 2. Characteristic TG (a) and DTG (b) curves of pyrolytic precursor activation by pyrolysis: ◆, PP1 (CC1); −, PP1 (CC2); +, PP1 (CC3); ■, PP2 (CC4); ▲, PP3 (CC5).

Table 1. Characteristics of Pyrolytic Precursor and Carbon-Supported Nickel Catalyst pyrolytic precursor

dP (mm)

cNi,PP (%)

dNi(c),PP (nm)

supported catalyst

tmax (°C)

cNi,CC (%)

dNi(c),CC (nm)

dNi,CC (nm)

SBET (m2/g)

ε

dmn = 2rmn (nm)

PP1 PP1 PP1 PP2 PP3

8 8 8 4 2

3.40 3.40 3.40 9.52 6.97

7.9 7.9 7.9 4.3 7.1

CC1 CC2 CC3 CC4 CC5

750 680 600 750 750

4.92 3.77 3.56 22.80 25.41

29 17 14 30 26

43 23 21 50 55

291 99 92 355 379

0.27 0.15 0.13 0.56 0.60

18.0 14.0 12.8 20.2 22.0

fraction, m/m0, and material mass loss rate, −d(m/m0)/dτ, vs logarithmic mean temperature between bed center and column wall, tm, are shown in Figure 1. A mass loss of cca. 70% for all fresh precursors (P1, P2, and P3) at the end of the pyrolysis process is observed in Figure 1a. Each differential curve in Figure 1b has a small peak between 90 and 140 °C and a relevant peak in the range of 140−350 °C. The mass loss up to 140 °C (about 9% for P2 and 16% for P1 and P3) is associated with moisture removal, whereas above 140 °C, it is mainly due to starch degradation.41−44,49 According to other findings,24,41,50 the pyrolysis of impregnated vegetal materials develops intensely in a main stage. The relevant peak corresponding to this stage is characterized by amplitudes ranging from 0.028 to 0.055 min−1 and temperatures in the field of 205−287 °C. Data in Figure 1b highlight that the peak temperature increases and its height decreases with increasing corn grain size.

Characterization of Pyrolytic Precursor Thermal Behavior during the Pyrolysis. TG and DTG curves registered for pyrolytic precursor activation by slow pyrolysis from the ambient temperature to a maximum activation temperature, tmax (600, 680, and 750 °C), under carbon dioxide flow are shown in Figure 2. Each differential curve in Figure 2b has three peaks, the first up to 230 °C, the second in the range of 230−560 °C, and the third between 560 °C and tmax. The mass loss up to 560 °C was about 30% for all pyrolytic precursors, whereas at the end of the activation process, the mass variations were as follows: 41−50% for PP1 activated at tmax = 600−750 °C and 61% and 63% for PP2 and PP3 activated at tmax = 750 °C. The mass loss up to 230 °C (cca. 7%) is associated with moisture removal; from 230 to 560 °C it can be an effect of residual volatiles removal, whereas above 560 °C it is probably due to an enhancement of the aromatization degree in the pyrolyzed product and to an additional 1494


Article


Figure 3. Pore size distribution of carbon-supported nickel catalyst: (a) catalyst prepared by activation of PP1, PP2, and PP3 precursors at 750 °C; (b) catalyst prepared by activation of PP1 precursor at 750 °C, 680 °C, and 600 °C.

Figure 4. XRD patterns of pyrolytic precursor.

activation temperature, tmax, in the order CC3 < CC2 < CC1 < CC4 < CC5. Pore size distribution of carbon-supported catalysts is depicted in Figure 3. Characteristic curves of supported catalysts activated at tmax = 750 °C (CC1, CC4, and CC5) highlight a narrow diameter distribution of small mesopores (4−8 nm) as well as a broad diameter distribution of larger mesopores (8−50 nm) and macropores (>50 nm) (Figure 3a). Moreover, the volume of mesopores and macropores is significantly larger for CC4 and CC5. For catalysts prepared by activation of PP1 precursor (dP = 8 mm) at tmax = 680 °C (CC2) and tmax = 600 °C (CC3), a broader diameter distribution of small mesopores and a lower volume of mesopores and macropores is observed (Figure 3b). A mean pore diameter, dmn, was estimated on the basis of pore size distribution data. The results listed in Table 1 show an increase

gasification in the presence of metallic nickel nanoparticles.40,51,52 As shown in Figure 2a, the final yield of carbonsupported catalyst decreased from 0.59 (CC3) to 0.37 (CC5) as the grain size diminished (dP = 8−2 mm) and activation temperature rose (tmax = 600−750 °C). Accordingly, it is expected to obtain the lowest values of textural parameters, nickel loading, and nickel particle size for CC3 catalyst (dP = 8 mm and tmax = 600 °C) as well as the highest values of catalyst properties for CC5 (dP = 2 mm and tmax = 750 °C). Characterization of Porous Structure. Analysis of BET surface area of pyrolytic precursors revealed values lower than 1 m2/g; therefore, the precursors were further activated to obtain carbon-supported catalysts with a highly developed porosity. The values of supported catalyst surface area, SBET, and porosity, ε, which are given in Table 1, emphasize an increase in SBET and ε with decreasing corn grain size, dP, and increasing 1495


Article


Figure 5. XRD patterns of carbon-supported nickel catalyst.

Figure 6. TEM images of carbon-supported nickel catalyst.

1 show the higher nickel loading of pyrolytic precursor, cNi,PP, the lower crystallite size, dNi(c),PP. XRD patterns of carbon-supported catalysts in Figure 5 have three narrow peaks (at about 44°, 52°, and 76°) indicating the presence of metallic nickel. The values of nickel crystallite size, dNi(c),CC, estimated by the Scherrer formula for the highest peak obtained at 44° and listed in Table 1, emphasize an increase in dNi(c),CC with tmax. Moreover, dNi(c),CC values are 1.8−7 times larger than those of dNi(c),PP, which can be attributed to the sintering of Ni crystallites from the pyrolytic precursor during its activation. TEM images of carbon-supported catalysts (Figure 6) highlight the presence of nickel nanoparticles embedded in the carbon matrix. The values of mean nickel nanoparticle diameter, dNi,CC, were estimated on the basis of results presented in the histograms of nickel particle size distribution (Figure 7). These values, which are listed in Table 1, are almost

in dmn with decreasing dP and increasing tmax in the order CC3 < CC2 < CC1 < CC4 < CC5. Determination of Nickel Loading. Characteristic values of nickel loading of pyrolytic precursor, cNi,PP, and carbonsupported nickel catalyst, cNi,CC, which are summarized in Table 1, indicate higher percent concentrations for supported catalyst, as effect of its lower mass. Moreover, an increase in cNi,CC with decreasing dP and increasing tmax is noticed, similar to the variation of textural parameters. Characterization of Nickel Crystallites and Particles. XRD patterns of pyrolytic precursors in Figure 4 contain two broad peaks, appearing at about 44° and 52°, which are attributed to the presence of metallic nickel. Values of nickel crystallite size, dNi(c),PP, of 7.9 nm (PP1), 4.3 nm (PP2), and 7.1 nm (PP3), respectively, were estimated by Scherrer formula for the highest peak, i.e., that obtained at 44°. Data given in Table 1496


Article


Figure 7. Histograms of nickel nanoparticle size distribution in carbon-supported nickel catalyst.

Figure 8. Nickel nanoparticle diameter, dNi,CC vs mean pore diameter, dmn, and BET specific surface area, SBET.

double those of nickel crystallites determined by XRD measurements, suggesting that a nanoparticle consists of two crystallites. Data summarized in Table 1 show an increase in dNi,CC with decreasing dP and increasing tmax, similar to SBET, ε, dmn, and cNi,CC variations. An increase in metal particle size with characteristic values of textural parameters was reported in the related literature.5,27 Moreover, dNi,CC varies linearly with dmn and SBET, as shown in Figure 8. Testing of Carbon-Supported Nickel Catalyst. The hydrogenation of cinnamaldehyde (CAL) consists of parallel and consecutive reduction of CC and CO functional groups yielding hydrocinnamaldehyde (HCAL) and cinnamyl alcohol (COL) as intermediate semihydrogenated products as well as hydrocinnamyl alcohol (3-phenyl propanol) (HCOL) as the final fully hydrogenated product (Figure 9). Catalyst performances in terms of CAL conversion, CCAL, and product selectivity, SHCAL, SCOL, and SHCOL, are compared in Figure 10 and Table 2. Characteristic plots of supported nickel catalysts (Figure 10) show approximately constant values of selectivity to HCAL, SHCAL, a decrease in selectivity to COL, SCOL, and an increase in selectivity to HCOL, SHCOL, as CAL conversion increases from 0 to 80−90%, indicating a significant

Figure 9. Reaction pathway for CAL hydrogenation.

HCOL production by CC bond hydrogenation of COL molecules. On the other hand, for CAL conversion levels larger than 80−90%, almost constant or slightly increasing values of SCOL accompanied by a decrease in SHCAL and an increase in SHCOL is observed. This may be an effect of a steric impediment due to an increase in COL concentration on the catalytic surface determining a top-on adsorption of CAL and HCAL molecules and facilitating the CO hydrogenation.36 Consequently, the HCOL is prevalently produced by CO bond hydrogenation; therefore, an increase in its concentration as well as a decrease in HCAL concentration and an insignificant 1497


Article


Figure 10. CAL conversion and product selectivity vs time: ◇, CAL;

▲,

COL; ■, HCAL; ●, HCOL.

Table 2. Catalyst Performances at 50% CAL Conversion and after 8 h of Reaction reaction time and product selectivity at CCAL = 50%

CAL conversion and product selectivity after 8 h of reaction

catalyst

τ50 (min)

SHCAL (%)

SCOL (%)

SHCOL (%)

CCAL (%)

SHCAL (%)

SCOL (%)

SHCOL (%)

CC1 CC2 CC3 CC4 CC5

161 126 151 104 99

34 38 39 39 31

59 47 49 47 55

7 15 12 14 14

90 92 90 97 97

30.24 24.75 36.80 29.12 21.13

45.43 42.95 37.56 33.85 43.31

24.33 32.30 25.64 37.03 35.56

or slightly increasing variation in COL concentration can appear. Characteristic curves of product selectivity are similar to those obtained over a carbon-supported Pt catalyst under the following conditions: 75 °C temperature, 1.6 MPa hydrogen pressure, 0.16 mol/L initial CAL molar concentration, 207 initial CAL/Pt molar ratio, 0.1 L ciclohexane, and 800−1200 μm supported catalyst size.25

Table 2 contains experimental data concerning the reaction time and product selectivities at a CAL conversion level of 50% as well as CAL conversion and product selectivities after 8 h of reaction. Tabulated results emphasize values of reaction time at CCAL = 50% from 99 to 161 min. The lowest time value corresponds to CC5 catalyst having the highest values of textural parameters, nickel loading, and nickel nanoparticle size. Product selectivities at CCAL = 50% are invariant with respect to 1498


Article


linearly with dmn, according to the data found in the related literature.28

the supported catalyst type, and their mean values are as follows: 36.2% for HCAL, 51.4% for COL, and 12.4% for HCOL. These values reveal a higher activity toward CO bond hydrogenation leading to COL than CC bond attack forming HCAL. A nickel catalyst usually exhibits a high selectivity to HCAL due to a narrow d-band of nickel atom. Besides this effect of nickel electronic structure, in this case appears also a strong steric repulsion between large nickel nanoparticle (dNi,CC > 21 nm) and CAL phenyl group, facilitating a top-on adsorption of CAL molecules and CO bond hydrogenation.8,25,37 Accordingly, at 50% CAL conversion, the effect of steric repulsion is stronger than that of metal electronic structure. CAL conversions varying from 90 to 97% were obtained after 8 h of reaction over the supported catalysts. The highest value of CAL conversion, i.e., CCAL = 97%, corresponds to CC4 and CC5 catalysts having larger values of textural parameters, nickel loading, and nickel nanoparticle size, according to other findings.5,27 Comparing the product selectivities at CCAL = 50% with those obtained after 8 h of reaction (21.13−36.80% for HCAL, 33.85−45.43% for COL, and 24.33−37.03% for HCOL), a slight decrease in selectivity to semihydrogenated products accompanied by a significant increase in selectivity to fully hydrogenated product is noticed. Product distribution seems not to depend on supported catalyst structure. Characteristic data of catalytic activity in terms of initial reaction rate and turnover frequency (TOF) are summarized in Table 3. Initial TOF, TOF0, and TOF estimated at 50% CAL

TOF0 =

v0VNA S Ninsite

(2)

TOF50 =

[CAL]0 VNA 120S Ninsiteτ50

(3)

S Ni =

6VMNi[CAL]0 RρNi dNi,CC

(4)

Figure 11. Initial TOF, TOF0, vs mean pore diameter, dmn.

Table 3. Catalytic Activity in Terms of Initial Reaction Rate and Turnover Frequency supported catalyst

106 × v0,exp (mol/ Ls)

TOF0 (s−1)

TOF50 (s−1)

SNi (m2)

n

105 × k (s−1)

106 × v0,calc (mol/ Ls)

CC1 CC2 CC3 CC4 CC5

3.60 3.56 3.18 4.46 4.75

0.21 0.11 0.09 0.31 0.36

0.09 0.06 0.05 0.17 0.19

0.07 0.13 0.14 0.06 0.05

0.96 0.96 0.96 0.96 0.96

6.26 6.83 6.26 10.45 9.56

2.19 2.42 2.21 3.63 3.35

The reaction rate can be significantly influenced by the external and internal mass-transfer steps. If they are very fast, the mass-transfer resistance can be neglected and the chemical reaction is the rate-determining step. Some tests were performed in order to estimate the mass-transfer limitation contribution. Catalytic runs were conducted at stirring rates ranging from 1000 to 1500 rpm, and insignificant variations in CAL conversion and product selectivity were observed. Consequently, external mass transfer resistance can be considered as negligible. Internal diffusion effect was evaluated on the basis of the Weisz−Prater number for CAL, ΦW−P, expressed by eq 5, where dCC (m) is the catalyst particle diameter, De (m2/s) the effective diffusion coefficient, and n the reaction order with respect to CAL.18,25,53 De was estimated by eq 6, where DCAL,IPA (m2/s) represents the CAL diffusion coefficient in 2-propanol and ε is the catalyst particle porosity.25 DCAL,IPA was evaluated using Wilke and Chang correlation (7), where MIPA (g/mol) is the 2-propanol molecular mass, T (K) the absolute operation temperature, VCAL (cm3/mol) the CAL molar volume at normal boiling point, x the 2-propanol association parameter, and ηIPA (cP) the 2-propanol viscosity at operation temperature.18,25,54 VCAL was estimated taking into account the atomic volume of C, H, and O as well as the presence of benzene ring in the structure of CAL (C6H5CHCHCHO) molecule.54 According to characteristic parameters values of eqs 5−7, which are summarized in Table 4, ΦW−P numbers less than 0.15 (0.001− 0.022) were obtained for the highest values of experimental initial reaction rate (v0 = 4.75 × 10−6 mol/Ls) and reaction order (n = 1), indicating an insignificant contribution of internal mass transfer.18

conversion, TOF50, defined as number of CAL molecules converted per surface Ni atom and per second (s−1), were estimated using correlations (2) and (3) depending on the following parameters: experimental initial rate, v0 (mol/Ls), initial CAL molar concentration ([CAL]0 = 0.03 mol/L), reaction volume (V ≈ VIPA = 0.1 L), Avogadro number (NA = 6.023 × 1023 molecule/mol), surface Ni atom (site) density (nsite = 14.6 × 1018 atom/m2 for the nickel atom having a metallic radius of 0.125 nm28), reaction time at 50% CAL conversion, τ50 (min), and total surface of nickel nanoparticles, SNi (m2). SNi was calculated by relationship (4), where MNi is the nickel molar mass (MNi = 58.7 g/mol), R the initial CAL/ Ni molar ratio (R = 40), ρNi the nickel density (ρNi = 8908 × 103 g/m3), and dNi,CC (m) the nickel nanoparticle diameter determined by TEM measurements. Data listed in Table 3 emphasize an increase in v0, TOF0, and TOF50 with decreasing dP and increasing tmax, similar to SBET, ε, dmn, cNi,CC, and dNi,CC variation, as well as an opposite trend for SNi. TOF values are consistent with results reported in other papers,14,37 and characteristic values of TOF0 are 1.7−2.3 larger than those of TOF50. Moreover, as shown in Figure 11, TOF0 increases 1499


Article


The carbon-supported nickel catalysts were characterized by various techniques, including nitrogen adsorption−desorption at 77 K to estimate the textural parameters (92−379 m2/g BET specific surface, 0.13−0.60 porosity, and 12.8−22 nm mean pore diameter), AAS to determine the nickel loading (3.56− 25.41%), and XRD and TEM to evaluate the size of nickel crystallite (14−30 nm) and nickel particle (21−55 nm). Experimental results suggested that a nickel nanoparticle consisted of two crystallites. Values of textural parameters, nickel loading, and nickel nanoparticle size increased as corn grain size decreased and activation temperature increased. The supported catalysts were reduced under hydrogen flow (ex situ) and then tested in the liquid-phase CAL hydrogenation. The process occurred under chemical control, and a first-order reaction with respect to CAL was established on the basis of experimental data. CAL hydrogenation performances were evaluated in terms of CAL conversion, TOF, and product selectivities. A linear increase in the initial TOF (0.09−0.36 s−1) with the mean pore diameter was obtained. A maximum catalytic activity, characterized by the best conversion (97%) and the largest TOF values, was attained for supported catalysts resulted from ground corn grains activated at 750 °C. Moreover, these catalysts exhibited the highest values of textural parameters, nickel loading, and nickel nanoparticle size. Poor selectivities to HCAL (21.13−36.80%) and COL (33.85− 45.43%), which may be attributed to antagonistic effects of nickel atom electronic structure and nickel nanoparticle size, were obtained after 8 h of reaction. Product distribution in the presence of various promoters added to the supported catalyst prepared from ground grains activated at 750 °C will be studied in future research.

Table 4. Weisz−Prater Number for CAL symbol

value

unit

MIPA ηIPA VCAL T x DCAL,IPA ε De dCC [CAL]0 v0 n ΦW−P

60 0.71 155.2 333 1−2.6 1.30−2.10 × 10−9 0.13−0.60 0.22−7.57 × 10−10 0.00033 0.03 3.18−4.75 × 10−6 0−1 0.001−0.022

g/mol cP cm3/mol K

ΦW−P =

m2/s m2/s m mol/L mol/Ls

2 v0dCC ⎛ n + 1⎞ ⎜ ⎟ 36De[CAL]0 ⎝ 2 ⎠

(5)

De = ε 2DCAL,IPA DCAL,IPA = 7.4 × 10−12

(6)

(xMIPA )0.5 T 0.6 ηIPA V CAL

(7)

In the absence of mass-transfer limitations, the reaction rate, v, can be expressed depending on CAL molar concentration, [CAL], as v=−

d[CAL] = k[CAL]n dt

■

(8)

The logarithmic form of expression (8) is ⎛ d[CAL] ⎞ ⎟ = log k + n log[CAL] log v = log⎜ − ⎝ dt ⎠

* Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b04059.

(9)

Values of reaction rate constant, k, and reaction order, n, which were obtained from the intercept and the slope of the

(

straight line given by a plot of log −

d[CAL] dt

■

) vs log[CAL] are

listed in Table 3. Tabulated data indicate a reaction of first order with respect to CAL (n ≈ 1), according with other findings,8 as well as values of k about 1.5 times larger for CC4 and CC5 (ground grains) than for CC1−CC3 (whole grains). Table 3 contains also the values of initial reaction rate, v0,calc, estimated by eq 10. Percentage errors between experimental and predicted initial reaction rate less 39% were obtained.

■

v0,calc = k[CAL]0 n

ASSOCIATED CONTENT

S

Tables S1−3 (PDF)

AUTHOR INFORMATION

Corresponding Author

*Tel: +4021 402 38 10. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Mäki-Arvela, P.; Hájek, J.; Salami, T.; Murzin, D. Yu. Chemoselective hydrogenation of carbonyl compounds over heterogeneous catalysts. Appl. Catal., A 2005, 292, 1−49. (2) Acres, G. J. K.; Bird, A. J.; Jenkins, J. W.; King, F. The design and preparation of supported catalysts. In Catalysis; Kemball, C., Dowden, D. A., Eds.; Royal Society of Chemistry: London, 1981; Vol. 4, pp 1− 30. (3) Fechete, I.; Wang, Y.; Védrine, J. C. The past, present and future of heterogeneous catalysis. Catal. Today 2012, 189, 2−27. (4) Amorim, C.; Wang, X.; Keane, M. A. Application of hydrodechlorination in environmental pollution control: comparison of the performance of supported and unsupported Pd and Ni catalysts. Chin. J. Catal. 2011, 32, 746−755. (5) Cabiac, A.; Cacciaguerra, T.; Trens, P.; Durand, R.; Delahay, G.; Medevielle, A.; Plée, D.; Coq, B. Influence of textural properties of activated carbons on Pd/carbon catalysis synthesis for cinnamaldehyde hydrogenation. Appl. Catal., A 2008, 340, 229−235.

(10)

CONCLUSIONS Carbon-supported catalysts based on nickel as catalytically active metal and corn grains as support were prepared, characterized, and applied in the liquid-phase CAL hydrogenation. Fresh precursors were prepared by impregnation of whole (8 mm) and ground (4 and 2 mm) corn grains with nickel nitrate solution, and these precursors were further pyrolyzed obtaining pyrolytic precursors. In order to obtain supported catalysts with a well-developed porous structure, the pyrolytic precursors were activated by slow pyrolysis at three levels of maximum activation temperature (600, 680, and 750 °C). 1500


Article


mesoporous carbon supported Fe and Zn promoted Pt catalyst. Appl. Catal., A 2008, 339, 159−168. (26) Kong, M.; Fei, J.; Wang, S.; Lu, W.; Zheng, X. Influence of supports on catalytic behaviour of nickel catalysts in carbon dioxide reforming of toluene as a model compound of tar from biomass gasification. Bioresour. Technol. 2011, 102, 2004−2008. (27) Wang, H.; Shu, Y.; Zheng, M.; Zhang, T. Selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde over SiO2 supported nickel phosphide catalysts. Catal. Lett. 2008, 124, 219−225. (28) Ghampson, I. T.; Newman, C.; Kong, L.; Pier, E.; Hurley, K. D.; Pollock, R. A.; Walsh, B. R.; Groundie, B.; Wright, J.; Wheeler, M. C.; Meulenberg, R. W.; DeSisto, W. J.; Frederick, B. G.; Austin, R. N. Effects of pore diameter on particle size, phase, and turnover frequency in mesoporous silica supported cobalt Fischer−Tropsch catalysts. Appl. Catal., A 2010, 388, 57−67. (29) Hu, S.; Xue, M.; Chen, H.; Shen, J. The effect of surface acidic and basic properties on the hydrogenation of aromatic rings over the supported nickel catalysts. Chem. Eng. J. 2010, 162, 371−379. (30) Kovalenko, G. A.; Rudina, N. A.; Chuenko, T. V.; Ermakov, D. Yu.; Perminova, L. V. Synthesis of catalytic filamentous carbon by the pyrolysis of alkanes on alumina-silica foam supporting nickel nanoparticles. Carbon 2009, 47, 428−435. (31) Zangouei, M.; Moghaddam, A. Z.; Arasteh, M. The influence of nickel loading on reducibility of NiO/Al2O3 catalysts synthesized by sol-gel method. Chem. Eng. Res. Bull. 2010, 14, 97−102. (32) Li, B.; Dong, W.; Ren, Y.; Feng, A. Preparation and characterization of spherical nickel-doped carbonized resin as hydrogenation catalysts II. Thermal decomposition of resin and preparation of metal-doped catalysts with different nickel loadings. Carbon 2007, 45, 1219−1225. (33) Li, B.; Ren, Y.; Fan, Q.; Feng, A.; Dong, W. Preparation and characterization of spherical nickel-doped carbonaceous resin as hydrogenation catalysts I. Carbonization procedures. Carbon 2004, 42, 2669−2676. (34) Wilson, M. S.; Delariva, A.; Garzon, F. H. Synthesis of sub-2 nm ceria crystallites in carbon matrixes by simple pyrolysis of ion-exchange resins. J. Mater. Chem. 2011, 21, 7418−7424. (35) Pernicone, N.; Traina, F. Catalyst activation by reduction. Pure Appl. Chem. 1978, 50 (9−10), 1169−1191. (36) Breen, J. P.; Burch, R.; Gomez-Lopez, J.; Griffin, K.; Hayes, M. Steric effects in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol using an Ir/C catalyst. Appl. Catal., A 2004, 268, 267−274. (37) Gallezot, P.; Richard, D. Selective hydrogenation of α,βunsaturated aldehydes. Catal. Rev.: Sci. Eng. 1998, 40, 81−126. (38) Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed.; Kroschwitz, I., Ed.; John Wiley and Sons: New York, 1992; Vol. 6. (39) Zhao, Z. F.; Wu, Z. J.; Zhou, L. X.; Zhang, M. H.; Li, W.; Tao, K. Y. Synthesis of a nano-nickel catalyst modified by ruthenium for hydrogenation and hydrodechlorination. Catal. Commun. 2008, 9, 2191−2194. (40) Richardson, Y.; Blin, J.; Volle, G.; Motuzas, J.; Julbe, A. In situ generation of Ni metal nanoparticles as catalyst for H2-rich syngas production from biomass gasification. Appl. Catal., A 2010, 382, 220− 230. (41) Dobre, T.; Pârvulescu, O. C.; Ceatră, L.; Stroescu, M.; Stoica, A. Fixed bed pyrolysis of untreated and Ni (II) impregnated corn grains: experiment and modelling. U.P.B. Sci. Bull. Ser. B 2012, 74, 143−158. (42) Dobre, T.; Pârvulescu, O. C.; Iavorschi, G.; Stoica, A.; Stroescu, M. Catalytic effects at pyrolysis of wheat grains impregnated with nickel salts. Int. J. Chem. React. Eng. 2010, 8, 1968−1992. (43) Dobre, T.; Pârvulescu, O. C.; Rodriguez Ramos, I.; Ceatră, L.; Stroescu, M.; Stoica, A.; Mirea, R. Global reaction kinetics and enthalpy in slow pyrolysis of vegetal materials. Rev. Chim. (Bucharest) 2012, 63, 54−59. (44) Pârvulescu, O. C.; Dobre, T.; Ceatră, L.; Iavorschi, G.; Mirea, R. Characteristics of corn grains pyrolysis in a fixed bed reactor. Rev. Chim. (Bucharest) 2011, 62, 89−94.

(6) Cerro-Alarcón, M.; Guerrero-Ruíz, A.; Rodríguez-Ramos, I. Stereoselective hydrogenation of Paracetamol to trans-4-acetamidocyclohexanol on carbon-supported Ru-M (M = Co, Ni) bimetallic catalysts. Catal. Today 2004, 93−95, 395−403. (7) Díaz, K.; García, V.; Matos, J. Activated carbon supported Ni-Ca: Influence of reaction parameters on activity and stability of catalyst on methane reformation. Fuel 2007, 86, 1337−1344. (8) Galvagno, S.; Capanelli, G.; Neri, G.; Donato, A.; Pietropaolo, R. Hydrogenation of cinnamaldehyde over Ru/C catalysts: effect of Ru particle size. J. Mol. Catal. 1991, 64, 237−246. (9) Peng, F.; Fu, X. B. Direct vapor-phase carbonylation of methanol at atmospheric pressure on activated carbon-supported NiCl2-CuCl2 catalysts. Catal. Today 2004, 93−95, 451−455. (10) Sápi, A.; Rémiás, R.; Kónya, Z.; Kukovecs, Á .; Kordás, K.; Kiricsi, I. Synthesis and characterization of nickel catalysts supported on different carbon materials. React. Kinet. Catal. Lett. 2009, 96, 379− 389. (11) Wojcieszak, R.; Zieliski, M.; Monteverdi, S.; Bettahar, M. M. Study of nickel nanoparticles supported on activated carbon prepared by aqueous hydrazine reduction. J. Colloid Interface Sci. 2006, 299, 238−248. (12) Wu, W.; Xu, J. Liquid-phase hydrodechlorination of chlorinated benzenes over active carbon supported nickel catalysts under mild conditions. Catal. Commun. 2004, 5, 591−595. (13) Zhang, Q.; Wang, H.; Sun, G.; Huang, K.; Fang, W.; Yang, Y. Study of Ni/C catalysts for vapor phase carbonylation of ethanol. J. Nat. Gas Chem. 2008, 17, 355−358. (14) Li, Y.; Lai, G. H.; Zhou, R. X. Carbon nanotubes supported PtNi catalysts and their properties for the liquid phase hydrogenation of cinnamaldehyde to hydrocinnamaldehyde. Appl. Surf. Sci. 2007, 253, 4978−4984. (15) Li, Y.; Zhou, R. X.; Lai, G. H. Effect of transition metals (Cr, Mn, Fe, Co, Ni and Cu) on selective hydrogenation of cinnamaldehyde over Pt/CNTs catalyst. React. Kinet. Catal. Lett. 2006, 88, 105−110. (16) van der Lee, M. K.; van Dillen, A. J.; Bitter, J. H.; de Jong, K. P. Deposition precipitation for the preparation of carbon nanofiber supported nickel catalysts. J. Am. Chem. Soc. 2005, 127, 13573−13582. (17) Liu, P.; Xie, H.; Tan, S.; You, K.; Wang, N.; Luo, H. Carbon nanofibers supported nickel catalyst for liquid phase hydrogenation of benzene with high activity and selectivity. React. Kinet. Catal. Lett. 2009, 97, 101−108. (18) Toebes, M. L.; Nijhuis, T. A.; Hájek, J.; Bitter, J. H.; van Dillen, A. J.; Murzin, D. Yu.; de Jong, K. P. Support effects in hydrogenation of cinnamaldehyde over carbon nanofiber-supported platinum catalysts: Kinetic modelling. Chem. Eng. Sci. 2005, 60, 5682−5695. (19) Wang, C.; Qiu, J.; Liang, C.; Xing, L.; Yang, X. Carbon nanofiber supported Ni catalysts for the hydrogenation of chloronitrobenzenes. Catal. Commun. 2008, 9, 1749−1753. (20) Aygun, A.; Yenisoy-Karakas, S.; Duman, I. Production of granular activated carbon from fruit stones and nutshells and evaluation of their physical, chemical and adsorption properties. Microporous Mesoporous Mater. 2003, 66, 189−195. (21) Baquero, M. C.; Giraldo, L.; Moreno, J. C.; Suárez-García, F.; Martínez-Alonso, A.; Tascón, J. M. D. Activated carbons by pyrolysis of coffee bean husks in presence of phosphoric acid. J. Anal. Appl. Pyrolysis 2003, 70, 779−784. (22) El-Hendawy, A. A. Surface and adsorptive properties of carbons prepared from biomass. Appl. Surf. Sci. 2005, 252, 287−295. (23) Girgis, B. S.; El-Hendawy, A. A. Porosity development in activated carbons obtained from date pits under chemical activation with phosphoric acid. Microporous Mesoporous Mater. 2002, 52, 105− 117. (24) Suárez-García, F.; Martínez-Alonso, A.; Tascón, J. M. D. Pyrolysis of apple pulp: effect of operation conditions and chemical additives. J. Anal. Appl. Pyrolysis 2002, 62, 93−109. (25) Mahata, N.; Goncalves, F.; Pereira, M. F. R.; Figueiredo, J. L. Selective hydrogenation of cinnamaldehyde to cinnamyl alcohol over 1501


Article

Industrial & Engineering Chemistry Research (45) AOAC. Official Methods of Analysis (OMA) of the Association of Official Analytical Chemists, 19th ed.; Latimer, G. W., Jr., Ed.; AOAC Int.: Gaithersburg, MD, 2012. (46) Moroi, A.; Vartolomei, N.; Aruş, V. A.; Nistor, I. D.; Lazăr, I. M. Prediction of the ash content of wheat flours using spectral and chemometric methods. AUDJG−Food Technology 2011, 35, 33−45. (47) Wang, P.; Singh, V.; Xu, L.; Johnston, D. B.; Rausch, K. D.; Tumbleson, M. E. Comparison of enzymatic (E-Mill) and conventional dry-grind corn processes using a granular starch hydrolyzing enzyme. Cereal Chem. 2005, 82, 734−738. (48) Watson, S. A. Structure and composition. In Corn: Chemistry and Technology; Watson, S. A., Ramstad, P. E., Eds.; American Association of Cereal Chemists: St. Paul, MN, 1987; pp 53−82. (49) Guinesi, L. S.; da Roz, A. L.; Corradini, E.; Mattoso, L. H. C.; Teixeira, E. M.; Curvelo, A. A. S. Kinetics of thermal degradation applied to starches from different botanical origins by non-isothermal procedures. Thermochim. Acta 2006, 447, 190−196. (50) Lu, C.; Song, W.; Lin, W. Kinetics of biomass catalytic pyrolysis. Biotechnol. Adv. 2009, 27, 583−587. (51) Bru, K.; Blin, J.; Julbe, A.; Volle, G. Pyrolysis of metal impregnated biomass: An innovative catalytic way to produce gas fuel. J. Anal. Appl. Pyrolysis 2007, 78, 291−300. (52) Di Blasi, C. Modeling chemical and physical processes of wood and biomass pyrolysis. Prog. Energy Combust. Sci. 2008, 34, 47−90. (53) Klaewkla, R.; Arend, M.; Hoelderich, W. F. A review of mass transfer controlling the reaction rate in heterogeneous catalytic systems. In Mass Transfer - Advanced Aspects; Nakajima, H., Ed.; InTech, 2011; pp 667−684; http://www.intechopen.com/books/ mass-transfer-advanced-aspects/a-review-of-mass-transfer-controllingthe-reaction-rate-in-heterogeneous-catalytic-systems. (54) Wilke, C. R.; Chang, P. Correlation of diffusion coefficients in dilute solutions. AIChE J. 1955, 1, 264−270.

1502


Preparation, Characterization, and Testing of a Carbon-Supported

Recommend Documents