Catalytic Decomposition of Pyrolysis Fuel Oil over in Situ Carbon

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Catalytic decomposition of pyrolysis fuel oil (PFO) over in-situ carbon-coated ferrierite zeolite for selective hydrogen production Jihyeon Kim, Gui Young Han, Jaeyoung Park, and Jong Wook Bae Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b04025 • Publication Date (Web): 27 Feb 2018 Downloaded from http://pubs.acs.org on March 1, 2018

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Submitted to the Energy & Fuels

Catalytic decomposition of pyrolysis fuel oil (PFO) over in-situ carboncoated ferrierite zeolite for selective hydrogen production

Jihyeon Kim, Gui-Young Han*, Jaeyeong Park, Jong-Wook Bae**

School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon, Gyeonggi-do, 440-746, Republic of Korea

---------------------------------------------------------------------------------------------------------------*Corresponding author (G.Y. Han): Tel.: +82-31-290-7249; Fax: +82-31-290-7272; E-mail address: [email protected] **Corresponding author (J.W. Bae): Tel.: +82-31-290-7347; Fax: +82-31-290-7272; E-mail address: [email protected]

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ABSTRACT Catalytic decomposition of pyrolysis fuel oils (PFO) for a selective production of hydrogen without any significant formation of greenhouse gas (CO2 and CH4) was investigated using ferrierite (FER) zeolites with different Si/Al molar ratios. The hydrogen production rate based on the feed moles of PFO was maximized on the FER having a Si/Al molar ratio of 10.4, and the hydrogen production rate on the FER zeolites was well correlated with their amounts of strong acid sites which easily form the active coke intermediates. An in-situ generated crystalline coke precursors on the acidic FER(10) surfaces having larger amounts of defect sites further played an important role as catalytic active sites for PFO decomposition and reforming reaction of CH4 generated as a main byproduct. The crystalline phases of the encapsulated graphitic carbon layers formed on the outer surfaces of the FER zeolites were strongly affected by their original acidic strengths, which simultaneously altered a steadystate hydrogen production rate with different product distributions of liquid-phase polycyclic aromatic components. A less amount of amorphous polyaromatic chemicals was formed on the most active FER(10) by easy decomposition reactions of the cracked intermediates from PFO. Although the initial activity of catalytic PFO decomposition was well correlated with the number of acidic sites of FER zeolites, the steady-state production rate of pure hydrogen was significantly affected by the newly formed surface coke properties on the carbonencapsulated FER such as its crystallinity and number of defect sites. The FER(10) showed a higher catalytic activity for PFO decomposition due to its abundant strong acidic sites and newly formed active graphitic carbon layers for a further CH4 reforming reaction.

Keywords: Pyrolysis fuel oils (PFO); Ferrierite (FER); Catalytic decomposition; Hydrogen; Active coke precursors.

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1. Introduction Since the increased concerns of significant global warming problems by CO2 emission through the combustion of fossil combustions, a lot of efficient technologies using alternative energy sources such as hydrogen and natural (or shale) gas have been intensively investigated.1-4 Hydrogen, one of alternative clean energy sources, can be a major energy carrier as a clean and renewable fuel,3 which has been largely used as an important reduction agent for many hydrotreating processes in refinery and petrochemical industries. The commercialized hydrogen production processes are mostly based on various hydrocarbon reforming reactions with subsequent catalytic processes such as water gas shift (WGS) and preferential oxidation reaction.5 However, all these processes inevitably produced a lot of green-house gases (GHG) such as CO2 mainly.6-8 To overcome these disadvantages of the commercialized reforming processes by reducing CO2 emission, many technologies such as decomposition of water by electrochemistry or photocatalysis and pyrolysis of hydrocarbons with co-production of carbon black and so on have been proposed as alternative ones. Among them, a direct decomposition of hydrocarbons into pure hydrogen and carbon materials can effectively eliminate the CO2 emission,3 which seems to be one of economically feasible processes using various carbon or metal oxide catalysts2-4,9,10 compared to the environmentbenign water splitting reaction. Among the available hydrocarbons for a direct decomposition reaction, pyrolysis fuel oils (PFO) byproduct mainly containing a wide-range of polycyclic aromatic hydrocarbons produced from naphtha cracking center (NCC) can be an economically feasible feedstock.11 The PFO can selectively produce pure hydrogen with a simultaneous production of solid cokes by the simplified reaction of CnHm → nC + (m/2)H2 on various heterogeneous solid-acid catalysts such as ZSM-5, Y or ferrierite (FER) zeolites having regular micropores with large amounts of acidic sites. In addition, the acidic sites of zeolites can be easily modified and controlled using an ion-exchange method with various 3


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metal ions according to the types of catalytic reactions to enhance catalytic activity and stability.12-15 Since the amount and strength of the acid sites on the zeolites can be easily adjusted according to molar ratios of Si/Al.16-18 the effects and roles of the surface acidity to catalytic activity and stability have been largely investigated for various catalytic reactions related with the severe depositions of coke precursors. Interestingly, many carbon materials such as carbon black and carbon nanotube having surface defect sites have been recently investigated as active heterogeneous catalysts for the decomposition of hydrocarbons to produce pure hydrogen without significant production of CO2.19-23 Especially, FER zeolite was selected as a candidate for PFO pyrolysis due to its relatively planar pore structures composed of the 8-membered ring (8-MR) and 10-membered ring (10-MR) structures with a larger amount of moderate acidic sites compared to other zeolites such as ZSM-5 and Mordenite18,23-26, which seems to have a beneficial effect for a higher stability through a small formation of inactive heavy coke precursors. In the present study, the effects of surface acidity of the FER zeolite with different Si/Al molar ratios to catalytic decomposition of PFO were investigated to elucidate the roles of acidic sites for an in-situ encapsulation of coke precursors having different crystallinities and defect sites. These newly formed crystalline coke precursors also played as important active sites at steady-state for subsequent decomposition of PFO reactant as well as main CH4 byproduct formed. The different production rates of hydrogen during the catalytic PFO decomposition according to different acidity of home-made pristine FER zeolites and roles of the newly formed crystalline coke precursors to steady-state catalytic activity have not been well studied till now as far as we know. The initial active sites from acidic sites of FER zeolites significantly altered the numbers of defect sites of the crystalline coke precursors encapsulated on the FER surfaces, which simultaneously changed the steady-state activity on the various types of coke surfaces. 4


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2. Experimental sections 2.1 Catalyst preparation and catalytic decomposition experiments of PFO Various home-made FER zeolites were previously synthesized as Na+-form FER with different Si/Al molar ratios from 8 to 20 by a hydrothermal synthesis method.18 For more details, the mixed solution of SiO2/NaAlO2/SDA/NaOH/deionized water (DIW) was prepared at a molar ratio of 1:y:0.9:0.14:40 (where, y value was changed according to Si/Al molar ratios of FER) by using the precursors of fumed silica (SiO2), sodium aluminate (NaAlO2), and piperidine (hexahydropyridine, C5H11N) as the sources of silica and alumina and structure-directing agent (SDA) for the synthesis of the FER zeolites, respectively. The mixed solution was completely stirred for more than 12 h and it was further used to synthesize the Na+-form FER zeolites in a batch reactor for 7 days. To exchange the Na ions to proton-type, the Na+-form FER zeolites were stirred in a 1 M NH4NO3 solution at 80 oC completely followed by washing it for 6 times using deionized water. Subsequently, the treated FER was calcined at 550 oC at a ramping rate of 1 oC/min for 3 h duration. As-prepared H-form FER was denoted as FER(x), where x represents Si/Al molar ratios from 8.1 – 20.0, which were also further confirmed by XRF analysis. To verify the activity of the home-made pristine FER zeolites, a commercially available reference FER zeolite having a higher Si/Al molar ratio of 20 in the form of NH4+-FER (Zeolyst (CP914C)) was also used after an activation under air flow at 550 oC for 3 h to transform it to H-form FER zeolite, and it was denoted as CFER. Catalytic decomposition activity of PFO was measured in a fixed-bed quartz tubular reactor with dimensions of 14.5 mm (inner diameter) x 640 mm (length) (reactor volume of 106 cm3) with a catalyst-bed height of 5 mm. As schematically represented in supplementary Figure S1, a central part of a quartz reactor was partially squeezed like a bottle-neck shape to 5


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prevent a slip-over of catalyst particles under a flow of vapor PFO reactant. The catalyst sample of 0.3 g was loaded on the quartz wool to fix the position of the loaded catalyst, and the reaction temperature was adjusted by using a 1/8-inch K-type thermocouple just on the top of the catalyst-bed in a quartz reactor heated by an electric furnace. A mixture of nitrogen carrier with vaporized PFO at a fixed amount of 15 mol% PFO injected by a high-pressure syringe pump was subsequently introduced under a N2 flow rate of 30 cm3/min into the reactor for PFO decomposition reaction, where the typical chemical compositions of commercially-available PFO11 are listed in supplementary Table S1. The catalytic decomposition reaction of the model PFO, which had a typical composition of naphthalene (31.4%), naphthalene derivatives (33.9%), fluorene (5.0%) and others (29.7%), was carried out for more than 60 min at the temperature of 700 - 850 oC and ambient pressure. The gaseous products formed were simultaneously analyzed at sampling intervals of 4 min using two on-line gas chromatographs (GC). A first on-line GC (Acme 6000M, YoungLin) was installed with a Carboxen 1006 column (Supelco) with Ar carrier gas to analyze main exit gases such as H2, N2, CO and CH4, and second on-line GC (Acme 6100, YoungLin) was equipped with a Hayesep Q column with He carrier gas to analyze cracked hydrocarbons from PFO such as CH4, C2H4 and C2H6, where a thermal conductivity detector (TCD) was used to analyze the gaseous products from the exit of reactor.

2.2 Catalyst Characterization High-power powder X-ray diffraction (XRD) patterns of the fresh and used FER zeolites were measured by suing D8 Advance X-ray diffractometer (Bruker) with a Cu Kα radiation of λ =1.5406 Å working at 40 kV and 100 mA with a scanning range of 2θ = 5 - 80° and scanning rate of 4 °/min to verify the crystalline structures of the characteristic FER zeolites. The relative crystallinity of FER zeolites was calculated by assuming a 100% crystallinity on 6


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the most crystalline FER(20) with the summed areas of the most intense two diffraction peaks at 2θ = 9.3 and 25.2o. The elemental compositions of the Si/Al molar ratios on the fresh FER zeolites were also measured by X-ray fluorescence (XRF) analysis by a Bruker S4 instrument operating at 60 kV and 150 mA. The surface acidity of the fresh FER zeolites was measured by temperature programmed desorption of NH3 (NH3-TPD) analysis at temperature range of 100 - 600 °C using a BELCAT-M instrument equipped with a TCD analyzer. For the NH3TPD analysis, the sample was previously treated at 350 oC for 1 h under He flow to remove any contaminants and water adsorbed on the surfaces. High-resolution transmission electron microscopy (HR-TEM) images on the selected FER(10) before and after PFO decomposition reaction were obtained by a transmission electron microscopy working at a voltage of 200 kV (JEM-2100F, JEOL), and the chemical compositions were also confirmed by EDS analysis. For an analysis of the coke precursors formed on the FER zeolites after PFO decomposition reaction at 750 oC, Raman analysis was carried out by using a dispersive Raman spectroscopy (Bruker FRA 160/S) on the used FER zeolites. Types of carbons and their binding energies (BE) of C 1s peaks on the used FER zeolites were measured by X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific K-ALPHA+) with a Al Kα X-ray source. The measured BEs were further corrected with the reference BE of C 1s (284.4 eV). The quantitative amount of coke precursors on the used FER zeolites was also verified by thermogravimetric analysis (TGA) of the used FER zeolites by using a Seiko Exstar 6000 (TG/DTA6100) instrument under air environment. In addition, the types of coke precursors on the surface FER zeolites with their structural stability were varied by using a Fourier transform infrared (FT-IR) spectroscopy analysis with a Perkin Elmer Spectrum 2000 spectrometer having a spectral resolution of 4 cm-1 equipped with a DTGS detector. Furthermore, the liquid/solid byproducts formed by catalytic decomposition reaction of PFO at 750 oC were analyzed by a GC-Mass spectrometer (GC-MS, Agilent 6890, 5973 MSD) 7


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installed with a HP-5MS UI column having the dimensions of 60 m x 0.25 mm x 0.25 um to confirm the chemical types of the polycyclic aromatic components.

3. Results and discussion 3.1. Catalytic activity of FER zeolites for decomposition of PFO The catalytic activities of PFO decomposition on the FER zeolites were summarized in Table 1 and their activity variations with time on stream (min) were displayed in Figure 1(A) and 1(B) at different reaction temperatures of 750 and 850 oC for 60 min. The extents of hydrogen production (mol/molPFO) as shown Figure 1(A) and 1(B) were steadily increased and stabilized after 30 min on stream on all the FER zeolites, except for the FER(20). Interestingly, the initial rates of PFO decomposition to approach steady-state values at 750 oC (Figure 1(A)) were found to be larger on the more acidic FER zeolites (i.e., steep slope of the hydrogen production), which followed by the order of FER(8) > FER(10) > FER(15) > FER(20). These trends are same with the changes of Si/Al molar ratios of FER zeolites, which were confirmed by XRF analysis as summarized in Table 1. Therefore, the induction period of hydrogen production rates on the FER zeolites at an initial stage was strongly affected by the number of active acidic sites on the pristine FER zeolites by selectively forming various active coke surfaces.23,24 However, the extent of hydrogen production at a steady-state was maximized on the FER(10) with the value of 0.90 mol/molPFO (Table 1) at 750 oC by showing a volcano-pattern according to Si/Al molar ratios of the FER zeolites in the range of 0.71 – 0.90 mol/molPFO. On the FER(8) showing the highest initial decomposition rate, a relatively smaller hydrogen production of 0.80 mol/molPFO at a steadystate seems to be attributed to the fast deactivation of the acidic sites by being fast covered with inactive coke precursors. The fast deactivation of the FER(8) was occurred by a rapid decrease of hydrogen production after 20 min as shown in Figure 1(A). On all the FER 8


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zeolites, the trends of CH4 production (main byproduct with a trace amount of C2 hydrocarbons) by PFO decomposition were found to be similar with the PFO decomposition rates as shown in supplementary Figure S2 (inset figure in Figure 1(A)), except for the FER(8). This observation seems to be attributed to the fast deposition of inactive carbonaceous species. The similar steady-state CH4 production rates on all the FER zeolites with their significantly different initial rates suggest that the active sites for PFO decomposition can proceed on two different sites with time on stream from the initially acidic sites on the FER zeolites to the surface defect sites of the active coke precursors formed possibly. However, the extent of hydrogen production at 850 oC was found to be similar on all the FER zeolites in the range of 1.88 – 2.02 mol/molPFO (Table 1) by showing the maximum value on the FER(10) as well as by maintaining a stable catalytic activity after 20 min as shown in Figure 1(B). In general, a faster reaction rate of PFO decomposition with a larger hydrogen production as well as larger amount of methane formation were typical characteristics with an increase of reaction temperatures on the CFER as shown in supplementary Figure S3. No significant plugging of reactor by heavy carbon depositions and complete conversion of PFO were clearly observed above the temperature of 800 oC. The methane byproduct can be formed by a facile liberation of substituted methyl groups in the polyaromatic hydrocarbons, which can be successively decomposed to hydrogen on the acidic sites.13 In addition, the catalytic decomposition of PFO on the FER zeolites was found to be much faster than noncatalytic thermal decomposition of PFO (almost one-third of the catalytic decomposition of PFO with a hydrogen production of ~0.60 mol/molPFO at 850 oC) as shown in Figure 1(B). These findings strongly suggest that the acidic sites of the FER zeolites play an important role for an initial decomposition of PFO by getting higher initial rates with an increase of total number of acidic sites of the FER zeolites. However, a steadystate hydrogen production by PFO decomposition seems not to be well related with the total 9


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acidic sites of the FER zeolites. This observation also suggests that the different active sites during the decomposition of PFO can be generated with simultaneous formations of different types of active coke precursors on the FER surfaces possibly, which can also act as the subsequent active sites for decomposition of main CH4 byproduct with a small amount of C2 hydrocarbons formed as shown in supplementary Figure S4. Based on the previous research results,19-22 the surface defect sites on carbon black (CB) acted as highly active sites for the decomposition of various hydrocarbons such as methane, propane and butane. Generally, the active sites for thermal decompositions of hydrocarbons on those carbonaceous materials have been proposed to be the unsaturated sites such as C=C bonds or vacant defect sites formed by the elimination of oxygenate complexes.20,23,27 We believe that the initially different activities of the decomposition of PFO on the FER zeolites according to the Si/Al molar ratios can selectively generate different crystalline phases of the deposited carbon precursors on the FER surfaces. The characteristics of coke precursors were also largely affected by the surface acid densities and strengths of the FER zeolites resulted with a different steady-state activity with a slightly different hydrogen production. Interestingly, these acidic site-derived crystalline coke precursors on the FER zeolites were found to be more active than the pristine carbon black material as shown in Figure 1(B), which seems to be beneficial effects for using those acidic zeolites for catalytic decomposition reactions of waste hydrocarbons. Therefore, the initial rates of PFO decomposition without significant deactivation, which were strongly affected by the acidic sites of the FER zeolites, can effectively control the types of newly formed carbon precursors and more active sites for the decomposition of PFO and that of intermediates (mainly CH4 byproduct) formed can be possibly generated. To verify these hypotheses of in-situ changes of active sites with time on stream on the FER zeolites, the various characterization tools to measure the acidity of the fresh FER zeolites and types of surface coke precursors formed during catalytic 10


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decomposition of PFO were further carried out by using XRD, NH3-TPD, TEM, Raman, XPS and FT-IR analysis.

3.2. Surface properties and active sites of the FER zeolites for decomposition of PFO The crystalline phases of the FER zeolites were measured by XRD analysis and their diffraction patterns are displayed in Figure 1(C). The characteristic pristine FER structures were well synthesized on all the FER zeolites and their relative crystallinities are summarized in Table 1. With an increase of Si/Al molar ratios, the most intense characteristic diffraction peaks at 2θ = 9.3 and 25.2o were increased steadily, which suggests an increased crystallinity by forming well-developed 8 and 10-MR micropore structures of the FER zeolite.25,28,29 The relative crystallinities were found to be in the range of 47 - 100%, where the FER(8) showed a lower crystallinity with the presence of abundant defect sites such as the Lewis acidic extraframework Al species possibly which were related with preferential formations of amorphous coke precursors.18,25 The surface acidity of the as-prepared FER zeolites was also verified by NH3-TPD analysis and desorption patterns of NH3 molecules are displayed in Figure 1(D). Two characteristic desorption peaks of NH3 were clearly observed at the maximum temperature range of 185 - 200 oC and ~440 oC, which can be assigned to weak and strong acidic sites, respectively. As summarized in Table 1, the amount of weak acidic sites was also gradually decreased with an increase of Si/Al molar ratios from 0.87 mmol/g on the FER(8) to 0.50 mmol/g on the FER(20), which were also found to be similar trends with the variation of total acidic sites as well. However, the strong acidic sites were maximized on the FER(10) with the value of 0.52 mmol/g, and other FER zeolites showed the less acidic sites in the range of 0.44 – 0.50 mmol/g. In general, these acidic site densities and strengths on the zeolites can largely change the extent of coke formations, which were well related with their crystallinity as well.25 More interesting points were that the initial activities of the 11


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decomposition of PFO were well correlated with total acidic sites by showing much fast reaction rate on the FER(8) having a largest acidic sites, and vice versa on the FER(20). This observation was well consistent with the Si/Al molar ratios of the FER zeolites as well. However, the hydrogen production rates at a steady-state were not well related with the total acidic sites of the fresh FER zeolites. Therefore, the newly and subsequently formed active coke precursors, which completely encapsulated the FER surfaces with their different crystallinities, seems to be possibly responsible for the different steady-state activities since the defect sites on the surface cokes such as carbon black19-22 and activated carbon30,31 can further play as effective active sites for various hydrocarbon decomposition reactions. In addition, these defect sites incorporated with Al species on the carbon matrix can also play an important role for the hydrocarbon decomposition reactions by newly generating acid sites,32 which can be possibly formed from some disintegrated FER structures during the high temperature PFO decomposition reaction. As shown in Figure 2(A) and supplementary Figure S5, the characteristic plate-like FER morphologies were clearly observed on the fresh FER(10) by TEM images. However, the completely encapsulated dense carbon layers on the outer surfaces of the FER(10) were also verified by TEM-EDS analysis, which had a layer thickness of ~ 40 nm in size as reported previously.33,34 The FER structures seem to be partially disintegrated by forming much thicker encapsulated carbon layers during the decomposition of PFO. The natures of the newly formed crystalline carbon layers on the FER surfaces, which can be assumed as new active sites, seem to be strongly altered by the acidic properties of the fresh pristine FER zeolites. The deposited thicker coke precursors on the used FER zeolites were found to be in the form of carbon spheres with their different sizes as shown in supplementary Figure S6 (inset TEM figure of the used FER(10)). TGA patterns on the used FER zeolites showed two oxidation steps as shown in Figure S6, and the first weight loss at 200 - 600 °C can be 12


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assigned to the acyclic hydrocarbons on the outer surfaces of the FER, and second one above 600 °C seems to be attributed to the inactive heavy carbonaceous materials such as carbon spheres.35,36 The amount of TGA weight loss below the temperate of 600 oC on the used FER zeolites were in the order of FER(10) > FER(15) > FER(20) > FER(8), which are well in line with the hydrogen production rates. As shown in Figure 2(B), the characteristic FER structures from XRD analysis on the used FER zeolites were partially disintegrated by showing a smaller XRD peak intensity, which seems to generate new acidic sites by strongly interacting with the coke precursors possibly. The newly observed two broad peaks at 2θ = 25 and 43o were attributed to the diffractions of (002) and (101) or (001) planes of the surface graphite as well. It also suggests that the crystalline FER structures can be distorted irregularly during the decomposition reaction of PFO and then the crystalline coke precursors can be covered on the FER zeolites.37,38 To further verify the coke precursors on the FER surfaces, which can possibly generate new active sites for the decomposition of PFO in the present study, the solid products (crystalline white or brown-colored powder mixed with unreacted PFO after reaction) formed on the catalyst surfaces as well as in the reactor bottom region were analyzed by GC-MS after dissolving them in an acetone solvent. Compared with the typical chemical compositions of PFO reactant11 as precisely summarized in Table S1, which were also roughly analyzed in the present study with the chemical compositions of naphthalene (31.4%), naphthalene derivatives (33.9%), fluorene (5.0%) and others (29.7%), the solid products related with the active coke precursors were mainly composed of the naphthalene and its derivatives on all the FER zeolites with the respective composition ranges of 60.7 – 83.1% and 8.0 – 19.7%, except for the FER(8) as shown in Figure 2(C) and summarized in Table 1. The more precise chemical compositions of those coke precursors such as polycyclic aromatic products after the catalytic decomposition of PFO on the commercial FER zeolite (CFER) reacted at 850 oC, 13


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which has more planer 8-membered ring (8-MR) and 10-membered ring (10-MR) structures by more easily facilitating the transfer of reactants to the active sites than other zeolites such as ZSM-5 and Mordenite, were measured by GC-MS and summarized in supplementary Figure S7. The larger portions of coke precursors on the used FER zeolites can be originated from the naphthalene and its derivatives formed, and these coke precursors can possibly act to form the disordered crystalline graphitic carbons such as graphene layers formed on the outer surfaces of the FER zeolites as shown in TEM images in Figure 2(A). We strongly believe those encapsulated crystalline graphitic coke layers formed on the outer FER surfaces are responsible for a steady-state activity of hydrogen production even after significant coke depositions. Interestingly, the surface properties of these active coke precursors formed were also largely affected by the surface acidity of the FER zeolites. Therefore, the amounts of the acidic sites on the FER zeolites can affect initial activities for decomposition of PFO by selectively forming different coke precursors, where the abundant stronger acidic sites of FER zeolites seem to be more preferential for the larger amount of coke precursor depositions.25 The formed coke precursors originated from the naphthalene and its derivatives have been known to be active sites for the decomposition of PFO with the help of the newly generated disordered graphitic carbon layers. The extents of active carbon sites were strongly affected by the acidic sites of the original FER zeolites, and the FER(10) having the much larger amount of weak and strong acidic sites can preferentially form the active graphitic carbon layers resulted in the much higher steady-state hydrogen production rate. Additional coke precursor characterization through Raman, XPS and FT-IR analysis on the used FER catalysts were carried out to verify the roles and natures of the coke precursors formed on the outer surfaces of the FER zeolites, and the results are displayed and summarized in Figure 3 and Table 1. The characteristics of the deposited carbon layers on the used FER zeolites were verified by Raman analysis and their Raman spectra are displayed 14


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in Figure 3(A). In general, different types of coke precursors can be selectively formed on the heterogeneous catalyst surfaces after hydrocarbon decomposition reactions such as polymeric, filamentous, and graphitic carbons.39 These coke precursors can be clearly distinguished by Raman analysis through the Raman shifts. The peak at ~1330 cm-1 assigned to the D band can be originated from the disordered carbon defect sites such as graphene layers, and the peak at ~1580 cm-1 assigned to the G band can be attributed to the amorphous carbons of in-plane displacements or ideal graphitic layers, respectively.39-42 Therefore, the intensity ratios of the ID/IG as summarized in Table 1 can be related with the extent of surface defect sites originated from the disordered graphitic structures, and the ratios of the ID/IG were found to be in the range of 3.34 - 5.43 by showing the maximum value on the FER(10) with 5.43. These trends of the ID/IG ratios were also well correlated with the extents of the steady-state hydrogen production in the order of FER(10) > FER(15) > FER(8) > FER(20). These coke precursors further changed by the weight-gain of the cokes deposited after reaction, and the increment of the coke precursors formed on the used FER zeolites was found to be in the range of 0.486 – 0.718 gcarbon/gFER with a maximum value of 0.718 gcarbon/gFER on the most active FER(10) as summarized in Table 1. These findings are also in line with the results of Raman, TGA analysis and hydrogen production rates on the FER zeolites. We believe that a larger amount of the disordered defect sites from the deposited carbons (assigned to D band) on the FER(10) effectively acted as the new active sites for the decomposition of PFO.19-23 From the XPS analyses on the used FER zeolites as shown in Figure 3(B), the characteristic carbon peaks were only observed without any other peaks such as silicon and aluminum species on all the used FER zeolites reacted at 750 oC as shown in supplementary Figure S8. The observation strongly suggests the complete encapsulation of the surfaces of the FER zeolites with different types of coke precursors during the decomposition of PFO as confirmed by TEM and Raman analysis. The XPS C 1s spectra on 15


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the used FER zeolites were deconvoluted to the characteristic carbon peaks such as the aliphatic C-C at the BE of 284.8 eV and C=C carbons at that of 284.3 eV. These characteristic peaks were also mainly originated form the surface naphthalene and its derivatives formed during the decomposition of PFO. The peaks at much higher BEs can be attributed to the oxygenates formed from the surface hydroxy groups of the FER zeolites such as C-O (285.3 eV), C-O-C (286.5 eV), and O-C=O (288.8 eV).42 The much smaller peak intensity of the C-C carbon peak than that of the C=C carbon on the FER(10) revealed less amorphous carbon formations with larger defect sites from the graphitic carbon species as confirmed by Raman analysis. As shown in supplementary Figure S9, the FT-IR spectra on the fresh FER zeolites showed the characteristic absorption bands for the asymmetric and symmetric stretching bands of the surface siloxane groups appeared at 1220, 1097 and 792 cm-1 and M-O absorption bands at 450 cm-1 without any significant differences on all the FER zeolites.43 After the decomposition of PFO at 750 oC on the FER zeolites, these characteristic absorption peaks of siloxane groups significantly disappeared on the less active FER(15) and FER(20) zeolites compared with that of FER(10). This observation revealed that the preservations of the siloxane groups even after decomposition of PFO were also important to generate additional active sites originated from the defected crystalline coke precursors on the FER surfaces. In addition, the encapsulated coke precursors with abundant defect sites on the used FER zeolites seem to be less active than the pristine FER zeolites since the decomposition activity of PFO at 850 oC were found to be similar on all the FER zeolites, where the deposited coke precursors were mainly acted as the active sites as well. In summary, the pristine FER zeolites having the various Si/Al molar ratios can effectively generate the different types of active coke precursors during the decomposition of PFO. The newly formed defect sites originated from coke precursors can further play important active sites for the decomposition of PFO and that of CH4 byproduct at a steady-state as clearly 16


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confirmed by the results of XPS, Raman and TEM analysis, especially on the most active FER(10) compared to higher silica containing FER(20). Even though the initially active FER zeolites were deactivated fast, the crystalline defect sites from the encapsulated coke precursors formed by in-situ decomposition of PFO played as stable active sites for a stable hydrogen production, where the amounts of defect sited from the deposited coke precursors were also strongly affected by the initial molar ratio of Si/Al on the pristine FER zeolite by showing a higher activity on the FER(10).

4. Conclusions Selective production of pure hydrogen with an insignificant emission of CO2 by catalytic decomposition of pyrolysis fuel oils (PFO) was investigated by using ferrierite (FER) zeolites having different Si/Al molar ratios. The maximum hydrogen production was observed on the FER(10) having a larger amount of strong acidic sites as well as active coke precursors for a subsequent decomposition of CH4. The in-situ formed coke precursors encapsulated on the acidic FER zeolite surfaces acted as a catalytic active site for a stable production of hydrogen by a decomposition of PFO as well as by that of CH4 byproduct formed, which was a main byproduct with a trace amount of C2 hydrocarbons. The amounts of acid sites on the pristine FER significantly altered an initial hydrogen production rate by preferentially forming different types of active coke precursors. The newly formed surface coke intermediates originated from naphthalene and its derivatives were found to be active for PFO and CH4 decomposition by in-situ forming the disordered graphitic carbon layers. Theses formation of active and defected carbon sites were strongly affected by the original acidic sites on the FER zeolites. The observed higher activity on the FER(10) zeolite was mainly attributed to preferential formations of active and encapsulated graphitic carbon layers on the acidic sites 17


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of the used FER(10), which was resulted in a higher steady-state hydrogen production rate during the PFO decomposition reaction.

Acknowledgments This research was supported by the Basic Science Research program of the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT & Future Planning of the Korea government (Grant No: NRF-2014R1A1A2053 532 and 2017R1D1A1B03028214).

Reference (1) Steinberg, M. Fossil fuel decarbonization technology for mitigating global warming. Int. J. Hydrogen Energy 1999, 24, 771-777. (2) Xiaoding, X.; Moulijn, J. A. Mitigation of CO2 by Chemical Conversion: Plausible Chemical Reactions and Promising Products. Energy Fuels 1996, 10, 305-325. (3) Gaudernack, B.; Lynum, S. Hydrogen from natural gas without release of CO2 to the atmosphere. Int. J. Hydrogen Energy 1998, 23, 1087-1093. (4) Kim, A. R.; Lee, H. Y.; Cho, J. M.; Choi, J. H.; Bae, J. W. Ni/M-Al2O3 (M = Sm, Ce or Mg) for combined steam and CO2 reforming of CH4 from coke oven gas. J. CO2 Util. 2017, 21, 211-218. (5) Poirier, M. G.; Sapundzhiev, C. Catalytic decomposition of natural gas to hydrogen for fuel cell applications. Int. J. Hydrogen Energy 1997, 22, 429-433. (6) Lee, Y.; Jang, J. T.; Bae, J. W.; Yoon, K. J.; Han, G. Y. Thermo-catalytic decomposition of waste lubricating oil over carbon catalyst. Korean J. Chem. Eng. 2016, 33, 2891-2897. (7) Kogan, A. Direct solar thermal splitting of water and on-site separation of the products-II. 18


Page 18 of 28

Page 19 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Experimental feasibility study. Int. J. Hydrogen Energy 1998, 23, 89-98. (8) Muradov, N. Z. How to produce hydrogen from fossil fuels without CO2 emission. Int. J. Hydrogen Energy 1993, 18, 211-215. (9) Zardin, L.; Perez-Lopez, O. W. Hydrogen production by methane decomposition over CoAl mixed oxides derived from hydrotalcites: Effect of the catalyst activation with H2 or CH4. Int. J. Hydrogen Energy 2017, 42(12), 7895-7907. (10) Yuan, L.; Ye, T.; Gong, F.; Guo, Q.; Torimoto, Y.; Yamamoto, M.; Li, Q. Hydrogen Production from the Current-Enhanced Reforming and Decomposition of Ethanol. Energy Fuels, 2009, 23(6), 3103-3112. (11) Lee, J.; Park, S. K. Synthesis of Carbon Materials from PFO, Byproducts of Naphtha Cracking Process. Appl. Chem. Eng. 2011, 22, 495-500. (12) Zhan, H.; Huang, S.; Li, Y.; Lv, J.; Wang, S.; Ma, X. Elucidating the nature and role of Cu species in enhanced catalytic carbonylation of dimethyl ether over Cu/H-MOR. Catal. Sci. Technol. 2015, 5, 4378-4389. (13) Reule, A. A. C.; Semagona, N. Zinc Hinders Deactivation of Copper-Mordenite: Dimethyl Ether Carbonylation. ACS Catal. 2016, 6, 4972-4975. (14) Wang, S.; Guo, W.; Zhu, L.; Wang, H.; Qiu, K.; Cen, K. Methyl Acetate Synthesis from Dimethyl Ether Carbonylation over Mordenite Modified by Cation Exchange. J. Phys. Chem. C 2015, 119, 524-533. (15) Zhou, H.; Zhu, W.; Shi, L.; Liu, H.; Liu, S.; Xu, S.; Ni, Y.; Liu, Y.; Li, L.; Liu, Z. Promotion effect of Fe in mordenite zeolite on carbonylation of dimethyl ether to methyl acetate. Catal. Sci. Technol. 2015, 5, 1961-1968. (16) Xu, B.; Bordiga, S.; Prins, R.; Van Bokhoven, J. A. Effect of framework Si/Al ratio and extra-framework aluminum on the catalytic activity of Y zeolite. Appl. Catal., A 2007, 333, 245-253. 19


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(17) Li, S.; Falconer, J. L.; Noble, R. D. SAPO-34 membranes for CO2/CH4 separations: Effect of Si/Al ratio. Micropor. Mesopor. Mater. 2008, 110, 310-317. (18) Ham, H.; Kim, J.; Lim, J. H.; Sung, W. C.; Lee, D. H.; Bae, J. W. Selective ethanol synthesis via multi-step reactions from syngas: Ferrierite-based catalysts and fluidized-bed reactor application. Catal. Today 2018, 303, 93-99. (19) Yun, Y. H.; Lee, S. C.; Jang, J. T.; Yoon, K. J.; Bae, J. W.; Han, G. Y. Thermo-catalytic decomposition of propane over carbon black in a fluidized bed for hydrogen production. Int. J. Hydrogen Energy 2014, 39, 14800-14807. (20) Lee, S. Y.; Kwak, J. H.; Han, G. Y.; Lee, T. J.; Yoon, K. J. Characterization of active sites for methane decomposition on carbon black through acetylene chemisorption. Carbon 2008, 46, 342-348. (21) Lee, S. Y.; Kim, M. S.; Kwak, J. H.; Han, G. Y.; Park, J. H.; Lee, T. J.; Yoon, K. J. Catalytic characteristics of carbon black for decomposition of ethane. Carbon 2010, 48, 2030-2036. (22) Yoon, S. H.; Park, N. K. Lee, T. J.; Yoon, K. J.; Han, G. Y. Hydrogen production by thermocatalytic decomposition of butane over a carbon black catalyst. Catal. Today 2009, 146, 202-208. (23) Ryu, B. H.; Lee, S. Y.; Lee, D. H.; Han, G. Y.; Lee, T. J.; Yoon, K. J. Catalytic characterization of various rubber-reinforcing carbon blacks in decomposition of methane for hydrogen production. Catal. Today 2007, 123, 303-309. (24) Muradow, N. Catalysis of methane decomposition over elemental carbon. Catal. Commun. 2001, 2, 89-94. (25) Park, S. Y.; Shin, C. H.; Bae, J. W. Selective carbonylation of dimethyl ether to methyl acetate on Ferrierite. Catal. Commun. 2016, 75, 28-31. (26) Dedecek, J.; Sobalik, Z.; Wichterlova, B. Siting and Distribution of Framework 20


Page 20 of 28

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Aluminium Atoms in Silicon-Rich Zeolites and Impact on Catalysis. Catal. Rev.: Sci. Eng. 2012, 54, 135-223. (27) Moliner, R.; Suelves, I.; Lazaro, M. J.; Moreno, O. Thermocatalytic decomposition of methane over activated carbons: influence of textural properties and surface chemistry. Int. J. Hydrogen Energy 2005, 30, 293-300. (28) Li, B.; Xu, J.; Han, B.; Wang, X.; Qi, G.; Zhang, Z.; Wang, C.; Deng, F. Insight into Dimethyl Ether Carbonylation Reaction over Mordenite Zeolite from in-Situ Solid-State NMR Spectroscopy. J. Phys. Chem. C 2013, 117, 5840-5847. (29) Bhan, A.; Allian, A. D.; Sunley, G. J.; Law, D. J.; Iglesia, E. Specificity of Sites within Eight-Membered Ring Zeolite Channels for Carbonylation of Methyls to Acetyls. J. Am. Chem. Soc. 2007, 129, 4919-4924. (30) Lee, S. C.; Jang, J. T.; Kim, J.; Bae, J. W.; Yoon, K. J.; Han, G. Y. Stable syngas production by concurrent methane decomposition and carbon dioxide gasification with activated carbon. Sci. Adv. Mater. 2016, 8, 205-211. (31) Muradov, N.; Smith, F.; T-Raissi, A. Catalytic activity of carbons for methane decomposition reaction. Catal. Today 2005, 102, 225-233. (32) Bae, S. Y.; Jeon, S.; Lee, Y. H.; Lee, D. H.; Kye, H.; Bae, J. W. Dehydrochlorination of polyvinylchloride using Al-modified graphitic-C3N4. RSC Adv. 2016, 6, 20728-20733. (33) Xu, L.; Zhang, W.; Yang, Q.; Ding, Y.; Yu, W.; Qian, Y. A novel route to hollow and solid carbon spheres. Carbon 2005, 43, 1084-1114. (34) Yang, Y.; Liu, X.; Zhang, C. Y.; Guo, M.; Xu, B. Controllable synthesis and modification of carbon micro-spheres from deoiled asphalt. J. Phys. Chem. Solids 2010, 71, 235-241. (35) Xiaoya, G.; Yong, Z.; Baohua, Z.; Jinyang, C. Analysis of coke precursor on catalyst and study on regeneration of catalyst in upgrading of bio-oil. Biomass Bioener. 2009, 33, 14691473. 21


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(36) Karolina, W.; Xuecheng, C.; Krzysztof, K.; Jacek, M.;,Ryszard, J. K.; Ewa M. Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors. Nanoscale Res. Lett. 2012, 7, 269-273. (37) Yushin, G. N.; Hoffman, E. N.; Nikitin, A.; Ye, H.; Barsoum, W. M.; Gogotsi, Y. Synthesis of nanoporous carbide-derived carbon by chlorination of titanium silicon carbide. Carbon 2005, 43, 2075-2082. (38) Yang, X.; Li, M.; Guo, N.; Yan, M.; Yang, R.; Wang, F. Functionalized porous carbon with appropriate pore size distribution and open hole texture prepared by H2O2 and EDTA2Na treatment of loofa sponge and its excellent performance for supercapacitors. RSC Adv. 2016, 6, 4365-4376. (39) Delhaes, P.; Couzi, M.; Trinquecoste, M.; Dentzer, J.; Hamidou, H.; Vix-Guterl, C. A comparison between Raman spectroscopy and surface characterizations of multiwall carbon nanotubes. Carbon 2006, 44, 3005-3013. (40) Reshetenko, T. V.; Avdeeva, L. B.; Ismagilov, Z. R.; Pushkarev, V. V.; Cherepanova, S. V.; Chuvilin, A. L.; Likholobov, V. A. Catalytic filamentous carbon: Structural and textural properties. Carbon 2003, 41, 1605-1615. (41) Castañoa, P.; Elordia, G.; Olazara, M.; Aguayoa, A. T.; Pawelecb, B.; Bilbaoa, J. Insights into the coke deposited on HZSM-5, Hβ and HY zeolites during the cracking of polyethylene. Appl. Catal. B 2011, 27, 91-100. (42) Tian, W.; Gao, Q.; Tan, Y.; Yang, K.; Zhu, L.; Yang, C.; Zhang, H. Bio-inspired beehive-like hierarchical nanoporous carbon derived from bamboo-based industrial byproduct as a high performance supercapacitor electrode material. J. Mater. Chem. A 2015, 3, 5656-5664. (43) Caldeira, V. P. S.; Santos, A. G. D.; Pergher, S. B. C.; Costa, M. J. F.; Araujo, A. S. Use of a low-cost template-free ZSM-5 for atmospheric petroleum residue pyrolysis. Quim. Nova 22


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2016, 39(3), 292-297.

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Figure Captions Figure 1. Hydrogen production (molH2/molPFO) with time on stream by the catalytic decomposition of PFO over the FER zeolites at the reaction temperatures of (A) 750 oC, (B) 850 oC, (C) XRD patterns of the fresh FER zeolites and (D) NH3-TPD profiles of the fresh FER zeolites Figure 2. TEM images of the (A-1) fresh and (A-2) used FER(10) with its magnified images (inset figures), (B) XRD patterns of the used FER zeolites reacted at 750 oC, (C) results of GC-MS analysis of polycyclic aromatic products after the catalytic decomposition of PFO on the commercial FER zeolite (CFER) reacted at 850 oC Figure 3. Coke precursor analyses by the characterization of (A) Raman and (B) XPS C1s analysis on the used FER zeolites at the reaction temperature of 750 oC

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Table 1. Surface properties of the FER zeolites and their activities for the catalytic decomposition of PFO with product distributions NH3-TPD (acid sites, Raman Activity XRF XRDb mmolNH3/g) Coke a Notation deposition H2 productionc weak strong cyclic aromatic productsd (g Si/Al ratio crystallinity total (mol/mol ) carbon/gFER) ID/IG PFO (400 oC) (C10/C10+/C14&C16/others) (750 / 850 oC) FER(8) 8.1 47.6 0.87 0.49 1.36 0.80 / 1.92 39.8 / 22.7 / 17.0 / 20.5 0.598 4.52 FER(10) 10.4 65.2 0.78 0.52 1.30 0.90 / 2.02 83.1 / 8.0 / 2.4 / 6.5 0.718 5.43 FER(15) 14.5 60.2 0.62 0.50 1.12 0.87 / 1.88 62.9 / 10.4 / 16.4 / 16.3 0.638 4.92 FER(20) 20.0 100 0.50 0.44 0.94 0.71 / 2.00 60.7 / 19.7 / 4.6 / 15.0 0.486 3.34 a Ferrierite (FER) zeolites are denoted as the FER(x), where x represents the Si/Al molar ratios measured by XRF analysis. b Crystallinity of the FER zeolites was calculated by using the summed intensities of two characteristic diffraction peaks appeared at 2θ = 9.3 and 25.2o with the assumption of 100% crystallinity of the FER(20). c Average amount of the produced hydrogen on the FER zeolites was measured at T = 750 and 850 oC, and the extent of hydrogen production was represented as molH2/molPFO at a steady-state after 0.5 h on stream (reference: hydrogen production by noncatalytic thermal decomposition of PFO at 850 oC = 0.55 molH2/molPFO). d Cyclic aromatic products after the catalytic decomposition of PFO were analyzed by GC-MS, and the main products including unreacted PFO were found to be polycyclic aromatic hydrocarbons such as naphthalene (C10H8 denoted as C10), naphthalene derivatives such as methyl-, ethyl-, dimethyl- naphthalene (denoted as C10+), phenanthrene (C14H12 denoted as C14), fluorene (C16H10 denoted as C16) and other heavy polyaromatics (denoted as others). For the referenced compositions of PFO, the composition of PFO reactant was further analyzed by GC-MS and it was mainly composed of naphthalene (31.4%), naphthalene derivatives (33.9%), fluorene (5.0%) and others (29.7%).

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Figure 1. Hydrogen production (molH2/molPFO) with time on stream by the catalytic decomposition of PFO over the FER zeolites at the reaction temperatures of (A) 750 oC, (B) 850 oC, (C) XRD patterns of the fresh FER zeolites and (D) NH3-TPD profiles of the fresh FER zeolites

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Figure 2. TEM images of the (A-1) fresh and (A-2) used FER(10) with its magnified images (inset figures), (B) XRD patterns of the used FER zeolites reacted at 750 oC, (C) results of GC-MS analysis of polycyclic aromatic products after the catalytic decomposition of PFO on the commercial FER zeolite (CFER) reacted at 850 oC

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Figure 3. Coke precursor analyses by the characterization of (A) Raman and (B) XPS C1s analysis on the used FER zeolites at the reaction temperature of 750 oC

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Catalytic Decomposition of Pyrolysis Fuel Oil over in Situ Carbon

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