Article pubs.acs.org/EF
Enhanced Hydrogen Production by Steam Reforming of Acetic Acid over a Ni Catalyst Supported on Mesoporous MgO Xiaoxuan Yang, Yajing Wang, Meiwei Li, Baozhen Sun, Yuanrong Li, and Yuhe Wang* Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, Key Laboratory of Design and Synthesis of Functional Materials and Green Catalysis, Colleges of Heilongjiang Province, and College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin, Heilongjiang 150025, People’s Republic of China ABSTRACT: A series of Ni-based catalysts supported on different MgO supports were investigated for hydrogen production via steam reforming (SR) of acetic acid (HAc). Three types of NiO and MgO solid solutions were prepared by co-precipitation of Ni(NO3)2 and Mg(NO3)2, impregnation of Ni(NO3)2 on MgO, and impregnation of Ni(NO3)2 on mesoporous MgO (denoted as MgO-m), respectively. The Ni-based catalysts were prepared by reducing these solid solutions at 650 °C in 10% H2/Ar. N2 adsorption results showed that the Brunauer−Emmett−Teller (BET) surface area of NiO/MgO-m solid solution was 3.0 and 2.3 times that of NiO−MgO and NiO/MgO solid solutions, respectively. The Ni/MgO-m catalyst showed the best catalytic performance, and the H2 yield can be enhanced by ∼160% by using the Ni/MgO-m catalyst. Ni/MgO-m kept its high activity up to 20 h of reaction. Thermogravimetry (TG) results indicated that no significant change was observed for the amount of carbon deposits on used Ni/MgO-m after 3 h on stream. Two kind of carbon species were observed on used Ni/MgO-m in the temperature-programmed oxidation (TPO) test.
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INTRODUCTION Hydrogen as an ideal clean fuel has attracted increasing research attention.1 Currently, the majority of hydrogen is produced from fossil fuels by steam reforming (SR). However, utilization of fossil fuels released CO2, which has caused climate change concern.2 A renewable resource, such as biomassderived oils, is considered as a suitable hydrogen resource.3 It is known that bio-oils can be obtained through the fast pyrolysis of biomass. Hydrogen can be produced from bio-oils by catalytic SR.4 Bio-oils are composed of oil and water-rich phases. In general, organic acids, alcohols, and phenol are the main components of bio-oils.5,6 Therefore, SR of acetic acid (HAc) was considered as a model reaction for developing efficient catalysts for hydrogen production from bio-oils.7−9 Previous study showed that noble metal catalysts exhibited excellent activity and anti-coking performance in SR of biofuels.10 However, the high cost of noble metal catalysts limited their further applications. As a promising alternative catalyst, non-noble metal catalysts have been studied for hydrogen production by SR of organic compounds.11 It was found that nickel is an active component in SR of hydrocarbon because of its high activity in breaking the C−C bond and producing H2. Ni supported on metal oxide (e.g., Ni/alumina) was reported to be active initially for the SR of organic hydrocarbons. However, the Ni-based catalyst deactivated quickly as a result of carbon deposition and metal sintering.12 It is highly desired to develop a novel Ni-based catalyst with high resistance to coke deposition and Ni sintering. It is known that basic oxides can reduce carbon deposits on catalyst by increasing the adsorption of water on the catalyst support.13 Basic oxides have been used as additives to reduce carbon deposits.14 Moreover, an alkaline earth support is expected to increase the concentration of basic sites and strengthen the adsorption of CO2 on the catalyst. Adsorbed CO2 can react with the carbon species. Thus, the deposited carbon in the © XXXX American Chemical Society
reaction procedure can be effectively suppressed by the CO2(g) + C(s) ↔ 2CO(g) reaction. It was reported that the addition of basic metal oxides, such as MgO, could alleviate the carbon deposits by enhancing the gasification rate of carbon species on the MgO surface, thus improving the catalyst lifetime.13,14 Furthermore, it was known that the composition of the catalyst support also influenced the coke resistance of the catalyst.12 It was reported that the strong metal−support interaction in NiO and MgO solid solution inhibited the Ni sintering of Nibased catalysts.15,16 Therefore, MgO can be considered as an appropriate support for Ni-based catalysts for SR of organic alcohols or organic acids. It was known that NiO can be dispersed into the MgO matrix to form a solid solution.15 Thus, it can inhibit the accumulation of Ni particles on the surface of Ni-based catalysts and enhance Ni catalytic activity and stability. Another strategy for enhancing the activity and stability of a supported Ni catalyst is to increase the specific surface area and pore size of the support. It was well-known that a catalyst support with a high specific surface area could promote the active metal dispersion. In addition, the large pore size of the support improved the mass-transfer ability for reactants and products.17−19 According to the literature, highly dispersion of Ni metal particles can be achieved by loading metal Ni on the oxide supports with high surface areas.20 Therefore, mesoporous oxides are considered a suitable support. It was reported that MgO-coated SBA-15 has been used as a strong alkaline mesoporous support.21 However, this kind of mesoporous catalyst is generally used in the catalytic reaction without steam, such as the methane reforming of CO2. This is mainly because Received: November 6, 2015 Revised: February 1, 2016
A
DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels mesoporous SiO2 is not hydrothermally stable.22 As a result of the presence of steam in the SR of HAc at a relatively high temperature, we used mesoporous MgO (denoted as MgO-m) instead of MgO-coated SBA-15 as a support. In this work, MgO-m was prepared using CMK-3, a mesoporous carbon, as the hard template. NiO/MgO-m was prepared by impregnation, and then Ni/MgO-m was obtained after reduction. To illuminate the influence of MgO-m on the catalyst activity, conventional MgO was also prepared and used as the support of the Ni catalyst. In addition, a NiO−MgO solid solution was also prepared by co-precipitation of Ni(NO3)2 and Mg(NO3)2 in ammonium hydroxide. The Ni catalysts supported on different MgO supports were tested for hydrogen production from SR of HAc. The results showed that Ni supported on MgO-m exhibited the highest activity and stability.
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O2 (10 mL/min) and Ar (40 mL/min). The signals of CO2 and H2O during TPO were monitored by online mass spectrometry (OmniStar SD301). Hydrogen Production. HAc SR experiments were carried out in a fixed-bed continuous flow reactor made of quartz at atmospheric pressure. Prior to the reaction, 0.3 g of the NixMg1 − xO sample was located in the middle of the reactor and reduced at 650 °C with 10% H2/Ar for 1 h. Before reactants were introduced, N2 was used to clean the reaction system. Afterward, the mixture of H2O and HAc was pumped using a peristaltic pump into an evaporator preheated at 140 °C, and then the reactants were introduced continuously into the reactor at a rate of 45 mL/min using a N2 flow. The gas products were detected using a gas chromatograph (GC) equipped with a thermal conductivity detector and TDX-01 column. The liquid products were analyzed using the other GC equipped with a column of Porapak Q and a flame ionization detector. HAc conversion was defined as a molar ratio of reacted HAc to HAc through the catalyst bed in unit time. The H2 yield was defined as a molar ratio of generated H2 to reacted HAc in unit time. The carboncontaining gas product selectivity was defined as the fraction of carbon-containing gas produced with respect to the theoretical full conversion of HAc to carbon-containing gas product. The HAc conversion, H2 yield, and gas product selectivity were calculated as follows:
EXPERIMENTAL SECTION
Catalyst Preparation. In this work, the chemical formula of NiO and MgO solid solution is Ni0.12Mg0.88O. The procedures for preparing different catalysts were as follows: Ni/MgO-m. The wet impregnation method was used for preparing MgO-m, with an appropriate amount of Mg(NO3)2 aqueous solution onto ordered mesoporous carbon CMK-3, which was used as the hard template.23 CMK-3 was prepared according to the method reported in ref 24. The procedure was as follows: 1.0 g of CMK-3 was dispersed in 2.0 mL of 2.0 M Mg(NO3)2 aqueous solution and subsequently heated in air at 90 °C for 12 h. After washing with anhydrous ethanol, the sample was heated in air at 200 °C for 10 h and at 300 °C for 3 h. After that, the above procedure was repeated twice. Finally, the sample was calcined in air at 650 °C for 3 h to remove CMK-3, and MgO-m was obtained. After that, 2.0 g of MgO-m was dispersed in 20.0 mL of 0.15 M Ni(NO3)2 aqueous solution and stirred for 2 h, followed by drying at 120 °C for 12 h and calcining at 650 °C for 9 h in air. The produced solid solution was marked as NiO/MgO-m. The sample was then reduced in 10% H2/Ar at 650 °C for 1 h to obtain the Ni/MgOm catalyst. Ni/MgO. A total of 2.5 wt % NH3·H2O was slowly added to 100 mL of 2.0 M Mg(NO3)2 aqueous solution under stirring at pH 9−10. After 4 h, the precipitate was washed using deionized water, filtered, and dried at 120 °C for 12 h. Mg(OH)2 was calcined at 650 °C in air for 9 h to obtain MgO. The Ni/MgO catalyst was also obtained with the above procedure. Ni/NiO−MgO. A total of 2.5 wt % NH3·H2O was slowly added to an aqueous solution of 14 mL of 2.0 M Ni(NO3)2 and 100 mL of 2.0 M Mg(NO3)2 under stirring at pH 9−10 and formed a green suspension. After 4 h, the precipitate was washed using deionized water, filtered and dried at 120 °C for 12 h, and then calcined in air at 650 °C for 9 h. Subsequently, the product of NiO and MgO solid solution (denoted as NiO−MgO) was reduced in 10% H2/Ar at 650 °C for 1 h to obtain the Ni/NiO−MgO catalyst. Catalyst Characterization. X-ray powder diffraction (XRD) patterns were recorded by a D8 ADVANCE instrument (Germany). The characterization of N2 adsorption−desorption was carried out at −196 °C on the automatic adsorption instrument (NOVA, Quanta Chrome). Hydrogen temperature-programmed reduction (H2-TPR) was obtained using a PCA-1200 instrument equipped with a thermal conductivity detector. In a typical test, the catalyst sample (0.5 g) was loaded into a quartz reactor and pretreated to 120 °C for 0.5 h in Ar flow, followed by cooling to room temperature. The temperature was then raised to 650 °C in 10% H2/Ar at a constant heating rate of 15.5 °C/min and kept at 650 °C for 1 h, followed by cooling to room temperature in the reducing gas atmosphere. The coke was tested by burning the used catalysts in flowing air on the thermogravimetry (TG)/differential thermal analysis (DTA) analyzer (PE Diamond) at 9 °C/min up to 1000 °C in flowing air. The temperature-programmed oxidation (TPO) measurement was carried out by heating the used catalyst (50.0 mg) at 5 °C/min up to 750 °C in flowing mixed gases of
HAc conversion = [1 − n(HAc out)/n(HAc in)] × 100%
(1)
H 2 yield = n(H 2)/n(HAc reacted)
(2)
Scarbon‐containing gas product = n(carbon‐containing gas product)/[n(HAc consumed) × 2]
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× 100%
(3)
RESULTS AND DISCUSSION Catalyst Characterization. The XRD patterns at low angles for MgO-m and NiO/MgO-m are presented in Figure 1.
Figure 1. XRD patterns at low angles for (a) MgO-m and (b) NiO/ MgO-m solid solutions.
The XRD pattern of MgO-m exhibits an apparent diffraction peak at 1.43°. This indicates the presence of the mesoporous structure in prepared MgO-m. For the NiO/MgO-m solid solution, a diffraction peak appears at around 1.27°. This indicates that the mesoporous structure of MgO-m was basically kept during the formation of NiO/MgO-m solid solution. In addition, Figure 1 also shows that the XRD becomes weaker for NiO/MgO-m compared to that for MgOm. One possible reason is that the ordering of the mesoporous structure declined as a result of the migration of Ni2+ into the MgO matrix during the formation of NiO/MgO-m solid solution. B
DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Figure 2 shows the wide-angle XRD patterns of NiO and MgO solid solutions. It can be seen that these materials exhibit
Figure 4. Pore size distribution curves for (a) NiO/MgO-m, (b) NiO/ MgO, and (c) NiO−MgO solid solutions.
Figure 2. XRD patterns at wide angles for (a) NiO/MgO-m, (b) NiO/MgO, and (c) NiO−MgO solid solutions and (d) physical mixture of MgO and NiO.
Table 1. Physical Properties of NiO and MgO Solid Solutions Prepared Using Different Methods
the diffraction peaks at 62.3°, 74.7°, and 78.6°, which are attributable to the diffraction of MgO. The diffraction peaks at 62.9°, 75.4°, and 79.4° can be attributed to the diffraction of NiO.15 These XRD results can be used to identify the formation of NiO and MgO solid solution. In comparison to the XRD pattern of the physical mixture of MgO and NiO (see Figure 2d), no obvious NiO diffraction peaks were observed at the wide-angle XRD patterns for NiO/MgO-m, NiO/MgO, and NiO−MgO solid solutions, because NiO was welldispersed onto the MgO matrix during the formation of NiO and MgO solid solution.25 Figures 3 and 4 show N2 adsorption isotherms and pore size distribution curves for NiO/MgO-m, NiO/MgO, and NiO−
sample
BET surface area (m2/g)
pore size (nm)
pore volume (cm3/g)
MgO-m MgO NiO/MgO-m NiO/MgO NiO−MgO
72.2 28.6 66.0 28.7 22.1
5.80 0.80 4.37 0.32 0.20
0.41 0.04 0.35 0.17 0.08
MgO-m is 2.3 times as large as NiO/MgO. In addition, the pore sizes and pore volumes of NiO/MgO and NiO−MgO are also lower than those of NiO/MgO-m, as seen in Table 1. The H2-TPR experiments were performed to imitate the reductive process at 650 °C for 1 h. As presented in Figure 5,
Figure 3. N2 adsorption−desorption isotherm plots for (a) NiO/ MgO-m, (b) NiO/MgO, and (c) NiO−MgO solid solutions.
MgO solid solutions. The Brunauer−Emmett−Teller (BET) surface areas, pore sizes and pore volumes are listed in Table 1. It can be seen in Figure 3 that the isotherm of NiO/MgO-m shows a type IV adsorption hysteresis with a steep condensation at p/p0 = 0.8. The result of N2 adsorption also confirms that the presence of mesoporosity in NiO/MgO-m solid solution.23 In comparison, no hysteresis loops were observed for the other samples in curves b and c of Figure 3. As seen in Table 1, the NiO/MgO-m sample exhibits the highest BET surface area of 66.0 m2/g and the largest pore volume of 0.35 cm3/g compared to those of NiO−MgO and NiO/MgO samples. From Figure 4 and Table 1, the Barrett−Joyner− Halenda (BJH) pore size for NiO/MgO-m is 4.37 nm, which is in the range of a mesopore. For the BET surface area, NiO/
Figure 5. TPR for (a) NiO/MgO-m, (b) NiO/MgO, and (c) NiO− MgO solid solutions.
the reduction peaks of three curves were clearly observed. It was well-known that the areas of peaks were proportional to the reduction amount of nickel, revealing that NiO in the three samples could be reduced in this pretreatment prior to catalysis. Catalytic Reaction. The SR of HAc was investigated over different catalysts using mild experimental conditions (temperature, 550 °C; N2 flow rate, 45 mL/min; liquid flow rate, 5.2 mL/h; and S/C, 6 mol/mol). The results of hydrogen production on different catalysts are listed in Table 2. The C
DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels decomposition 1
Table 2. Results for Steam Reforming of HAc over Various Catalystsa
CH3COOH → CH4 + CO2
selectivity (%)
catalyst
HAc conversion (%)
H2 yield (mol/mol)
CO2
CO
Ni/MgO-m Ni/MgO Ni/NiO−MgO
90.3 79.2 66.3
2.9 1.1 0.9
16.4 25.3 25.1
11.9 20.6 21.7
decomposition 2 CH3COOH → 2H 2 + CO2 + C
CH4
CH3COOH → CH 2CO + H 2O
(8)
SR ketene CH 2CO + H 2O → 2CO + 2H 2
(9)
water-gas shift reaction (WGSR)
liquid products were only unconverted HAc and acetone (not shown here). The Ni/MgO and Ni/NiO−MgO catalysts exhibited low activities for the SR of HAc, and HAc conversions were 79.2 and 66.3%, respectively. The H2 yield on Ni/MgO and Ni/NiO−MgO were 1.1 and 0.9 mol/mol, respectively. The results showed that the catalyst prepared by the impregnation method was superior to the catalyst prepared by the co-precipitation method. It could be caused by the fact that the amount of active metal Ni sites in Ni/MgO catalysts was higher than that in Ni/NiO−MgO catalysts because the areas of reduction peaks for the former were larger than those for the latter (see Figure 5). Ni/MgO-m was tested for hydrogen production, and the results were also listed in Table 2. It can be seen that the Ni/MgO-m catalyst showed the best catalytic performance in HAc conversion and H2 yield compared to the other catalysts. This was attributed to the mesoporous structure of Ni/MgO-m. The large specific surface area facilitated the dispersion of Ni metal particles on the surface of the catalyst. The large pore size of the Ni/MgO-m catalyst favored the mass transfer of reactants.26 It is noted that the catalytic activity of Ni/MgO-m can be stabilized more than 20 h on stream. To compare our catalysts to other previously reported catalysts, the catalytic performance of several typical Ni−Mg catalysts was summarized in Table 3.27−29 HAc conversion, H2 yield, and stability of the catalyst were compared. As seen in Table 3, the Ni20Co80MgO catalyst exhibited the highest HAc conversion of ∼100% and a H2 yield of 3.1 mol/mol. In comparison to the other two catalysts, Ni/ MgO-m showed similar HAc conversion and H2 yield but at a much lower reaction temperature of 550 °C. These results indicate that Ni/MgO-m could be a promising catalyst for SR at lower temperatures. On the basis of available data, we concluded a plausible HAc SR reaction path combined with the literature.10
CO + H 2O → CO2 + H 2
(10)
First, HAc could take place in the ketonization reaction to form acetone on the Ni active sites, and then it could be reformed by the steam to produce H2 and CO. In addition, HAc was decomposed to form methane and carbon dioxide or hydrogen, carbon dioxide, and carbon. It was likely that ketene could be formed by dehydrating from HAc and subsequently be reformed by steam. However, above all, CO produced by combinations of transformation of intermediate can be eliminated by the WGSR. Catalyst Stability and Carbon Deposits. The stability of Ni/MgO-m was also tested, and Figure 6 shows the
Figure 6. (a) HAc conversion and (b) H2 yield versus reaction time over the Ni/MgO-m catalyst. Reaction conditions: catalyst, 0.3 g; temperature, 550 °C; N2 flow rate, 45 mL/min; liquid flow rate, 5.2 mL/h; and S/C, 6 mol/mol.
dependence of the HAc conversion and H2 yield on the reaction time on stream (TOS). As seen in Figure 6, the conversion of both reactants and H2 yield over Ni/MgO-m declined with the reaction time in the initial 7 h of reaction. After 7 h on stream, HAc conversion and H2 yield were almost unchanged and the activity of the catalyst was maintained after
ketonization (4)
SR acetone CH3COCH3 + 3H 2O → 3CO + 6H 2
(7)
dehydration
a Reaction conditions: catalyst, 0.3 g; temperature, 550 °C; N2 flow rate, 45 mL/min; liquid flow rate, 5.2 mL/h; S/C, 6 mol/mol; and TOS, 3 h.
2CH3COOH → CH3COCH3 + CO2 + H 2O
(6)
(5)
Table 3. Comparison for H2 Production over Several Typical Catalysts and Catalysts Prepared in This Work
a
catalyst
HAc conversiona (%)
H2 yieldb (mol/mol)
S/C (mol/mol)
temperaturec (°C)
stabilized TOSd (h)
reference
Ni20Co80MgO 15Ni5Mg/Al 5% Cu/Ni−Al−Mg Ni/MgO-m
∼100 91.0 94.3 90.3
3.1 2.7 3.0 2.9
8 4 5.6 6
600 600 650 550
20 24 10 20
27 28 29
HAc conversion after activity stabilized. bH2 yield (molar H2/molar HAc) after activity stabilized. cReaction temperature. dTOS = time on stream. D
DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels more than 20 h of reaction. The H2 yield was not reduced, and it was maintained at 2.7 mol/mol after 7 h of reaction. From the above results, it can be found that Ni/MgO-m exhibited good stability, which may be due to the use of MgO-m as the catalyst support, and the large pore for Ni/MgO-m favored the transport of the reactants and products. To illustrate the catalytic performance, TG, XRD, and TPO were used to characterize used Ni/MgO-m after reaction. The TG curves of used Ni/MgO-m were presented in Figure 7. It
on the Ni/MgO-m catalyst was almost unchanged before and after reaction. This is due to the strong interaction between metal Ni and the support of solid solution.15,16 In addition, a diffraction peak appeared at 26.2° for the used Ni/MgO-m catalyst. This XRD peak can be attributed to the diffraction peak of graphite carbon, which was deposited on the catalysts during the conversion of HAc.16 The TPO profiles of the used Ni/MgO-m catalysts are shown in Figure 9. The CO2 signals from the reaction of
Figure 7. TG patterns for the used Ni/MgO-m catalysts. The used catalysts were sampled after reaction for (a) 1 h, (b) 3 h (c) 7 h, and (d) 20 h.
Figure 9. CO2 signal versus temperature in TPO for the used Ni/ MgO-m catalysts. The used catalysts were sampled after reaction under temperature of 550 °C, N2 flow rate of 45 mL/min, liquid flow rate of 5.2 mL/h, and S/C of 6 mol/mol for (a) 1 h, (b) 3 h (c) 7 h, and (d) 20 h.
can be seen that the used catalysts exhibit obvious weight loss between 450 and 700 °C. This weight loss can be attributed to the combustion of carbon species, which was deposited on the Ni/MgO-m catalysts during the hydrogen production.16 We observed that the amount of carbon deposition increased with time for 1, 3, and 7 h of reaction. These results agree with the initial deactivation of the catalyst that we observed (see Figure 6). From TG results in Figure 7, it can also be seen that weight loss was constant on the used catalysts after 7 h of reaction, which means no more carbon deposition on the catalysts from 7 to 20 h of reaction. Figure 6 also exhibits the activity of the Ni/MgO-m catalyst stabilized from 7 to 20 h of reaction. Therefore, it can be concluded that the carbon species deposited on the used catalysts caused the initial deactivation of Ni/MgO-m in the SR of HAc. The XRD results of the fresh and used Ni/MgO-m catalysts are shown in Figure 8. It was found that the XRD peaks of metal Ni appeared at 44.5° and 52.0° for the fresh and used Ni/MgO-m. The similar intensity of diffraction peaks indicates that the size of Ni metal particles
oxygen and carbon deposits over used Ni/MgO-m can be observed between 500 and 700 °C. It was found that one CO2 signal centered at ∼610 °C and the other CO2 signal centered at ∼650 °C. The CO2 signals should be corresponding to two types of carbon species, which were marked as α and β, respectively.6 It can be estimated from the peak areas of CO2 in the TPO profiles that the amount of α carbon was almost unchanged with the TOS. However, the characteristic peak of β carbon was very weak when the reaction was carried out for 1 h. The amount of β carbon increasing with time can be estimated by measuring the CO2 peak area. After 7 h of reaction, the amount of β carbon was constant (see Figure 9). Therefore, it can be inferred that the α carbon species was less relevant to the stability of the Ni/MgO-m catalyst. On the contrary, the β carbon species was related to the stability of the catalyst. Simultaneously, the characteristic peak of water was observed between 500 and 600 °C in Figure 10. Hence, it shows that the composition of the carbon species contains H and C elements. On the basis of XRD and TG results (see Figure 7), it can be speculated that the composition of carbon deposits over used Ni/MgO-m may be a mixture of graphite and CxHy.
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CONCLUSION H2 production by SR of HAc as a model compound of bio-oil was investigated over Ni/MgO-m, Ni/MgO, and Ni/NiO− MgO catalysts. The results indicated that the Ni/MgO-m catalyst, using mesoporous MgO as the support, exhibited the highest catalytic activity among the studied catalysts. Ni/MgOm exhibited the highest specific surface area and largest pore size among the studied catalysts, which favored a high dispersion of metal Ni particle. It improved the transport of reactants and products and, subsequently, resulted in a high catalytic activity.
Figure 8. XRD patterns for the fresh and used catalysts of Ni/MgO-m. The used catalysts were sampled after reaction under temperature of 550 °C, N2 flow rate of 45 mL/min, liquid flow rate of 5.2 mL/h, and S/C of 6 mol/mol for (a) fresh catalyst, (b) 1 h, (c) 3 h, and (d) 7 h. E
DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels
(11) Marquevich, M.; Czernik, S.; Chornet, E.; Montané, D. Hydrogen from biomass: Steam reforming of model compounds of fast pyrolysis oil. Energy Fuels 1999, 13, 1160−1166. (12) Sugisawa, M.; Takanabe, K.; Harada, M.; Kubota, J.; Domen, K. Effects of La addition to Ni/Al2O3 catalysts on rates and carbon deposition during steam reforming of n-dodecane. Fuel Process. Technol. 2011, 92, 21−25. (13) Garcia, L.; French, R.; Czernik, S.; Chornet, E. Catalytic steam reforming of bio-oils for the production of hydrogen: effects of catalyst composition. Appl. Catal., A 2000, 201, 225−239. (14) Trane-Restrup, R.; Jensen, A. D. Steam reforming of cyclic model compounds of bio-oil over Ni-based catalysts: Product distribution and carbon formation. Appl. Catal., B 2015, 165, 117−127. (15) Ruckenstein, E.; Hang Hu, Y. Methane partial oxidation over NiO/MgO solid solution catalysts. Appl. Catal., A 1999, 183, 85−92. (16) Wang, Y. H.; Liu, H. M.; Xu, B. Q. Durable Ni/MgO catalysts for CO2 reforming of methane: Activity and metal-support interaction. J. Mol. Catal. A: Chem. 2009, 299, 44−52. (17) Tan, M. W.; Wang, X. G.; Shang, X. F.; Zou, X. J.; Lu, X. G.; Ding, W. Z. Template-free synthesis of mesoporous γ-aluminasupported Ni−Mg oxides and their catalytic properties for prereforming liquefied petroleum gas. J. Catal. 2014, 314, 117−131. (18) Meshkani, F.; Rezaei, M. Nickel catalyst supported on magnesium oxide with high surface area and plate-like shape: A highly stable and active catalyst in methane reforming with carbon dioxide. Catal. Commun. 2011, 12, 1046−1050. (19) Xu, L. L.; Song, H. L.; Chou, L. J. Carbon dioxide reforming of methane over ordered mesoporous NiO−Al2O3 composite oxides. Catal. Sci. Technol. 2011, 1, 1032−1042. (20) Zhang, H.; Li, M.; Xiao, P. F.; Liu, D. L.; Zou, C. J. Structure and catalytic performance of Mg-SBA-15-supported nickel catalysts for CO2 reforming of methane to syngas. Chem. Eng. Technol. 2013, 36, 1701−1707. (21) Wang, N.; Yu, X. P.; Shen, K.; Chu, W.; Qian, W. Z. Synthesis, characterization and catalytic performance of MgO-coated Ni/SBA-15 catalysts for methane dry reforming to syngas and hydrogen. Int. J. Hydrogen Energy 2013, 38, 9718−9731. (22) Chen, L. Y.; Jaenicke, S.; Chuah, G. K. Thermal and hydrothermal stability of framework-substituted MCM-41 mesoporous materials. Microporous Mater. 1997, 12, 323−330. (23) Roggenbuck, J.; Tiemann, M. Ordered mesoporous magnesium oxide with high thermal stability synthesized by exotemplating using CMK-3 carbon. J. Am. Chem. Soc. 2005, 127, 1096−1097. (24) Jun, S.; Joo, S. H.; Ryoo, R.; Kruk, M.; Jaroniec, M.; Liu, Z.; Ohsuna, T.; Terasaki, O. Synthesis of new, nanoporous carbon with hexagonally ordered mesostructure. J. Am. Chem. Soc. 2000, 122, 10712−10713. (25) Li, M. S.; Li, S. R.; Zhang, C. X.; Wang, S. P.; Ma, X. P.; Gong, J. L. Ethanol steam reforming over Ni/NixMg1‑xO: Inhibition of surface nickel species diffusion into the bulk. Int. J. Hydrogen Energy 2011, 36, 326−332. (26) Iwasa, N.; Yamane, T.; Takei, M.; Ozaki, J. I.; Arai, M. Hydrogen production by steam reforming of acetic acid: Comparison of conventional supported metal catalysts and metal-incorporated mesoporous smectite-like catalysts. Int. J. Hydrogen Energy 2010, 35, 110−117. (27) Zhang, F. B.; Wang, N.; Yang, L.; Li, M.; Huang, L. H. Ni−Co bimetallic MgO-based catalysts for hydrogen production via steam reforming of acetic acid from bio-oil. Int. J. Hydrogen Energy 2014, 39, 18688−18694. (28) Nogueira, F. G. E.; Assaf, P. G. M.; Carvalho, H. W. P.; Assaf, E. M. Catalytic steam reforming of acetic acid as a model compound of bio-oil. Appl. Catal., B 2014, 160−161, 188−199. (29) Bimbela, F.; Chen, D.; Ruiz, J.; García, L.; Arauzo, J. Ni/Al coprecipitated catalysts modified with magnesium and copper for the catalytic steam reforming of model compounds from biomass pyrolysis liquids. Appl. Catal., B 2012, 119−120, 1−12.
Figure 10. H2O signal versus temperature in TPO for the used Ni/ MgO-m catalysts. The used catalysts were sampled after reaction under temperature of 550 °C, N2 flow rate of 45 mL/min, liquid flow rate of 5.2 mL/h, and S/C of 6 mol/mol for (a) 1 h, (b) 3 h (c) 7 h, and (d) 20 h.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +86-451-8806-0570. Fax: +86-451-8632-9715. Email:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors are grateful for the financial support for this work provided by the Overseas Scholars Program of the Department of Education, Heilongjiang Province (1155h019), and the Program for Scientific and Technological Innovation Team Construction in University of Heilongjiang Province (2011TD010).
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DOI: 10.1021/acs.energyfuels.5b02615 Energy Fuels XXXX, XXX, XXX−XXX
