Steam Reforming Of Acetic Acid Research Articles

In-situ decomposition of citric acid for eliminating coking in steam reforming of acetic acid through enhanced gasification of coke precursors

H2O and CO2 are two important agents for gasification of precursors of coke in steam reforming (SR). Their in-situ formation from decomposition of reactant might facilitate removal of coke deposit from surface of catalyst. This was investigated in SR of acetic acid (HAc) mixed with presence of citric acid (CA) over Ni/SBA-15 catalyst, as CA could decompose to form simultaneously H2O and CO2 for potentially involving in gasification reactions. The results showed that CA presence could not enhance catalytic activity of Ni/SBA-15 but remarkably promoted the catalytic stability. This was due to effective suppression of coking by CA (42.3 % coke in SR of HAc versus ca. 10 % coke in co-reforming of HAc and CA and 6.7 % coke in SR of CA). The adsorbed *CO2 and *OH species produced in-situ by decomposition of CA effectively gasified the precursors of coke such as *CxHy and O-containing species like *CO and *C-O-C.

Synthesis of bentonite-supported Ni, La, and Ca catalysts for hydrogen production through steam reforming of acetic acid

In this study, the production of hydrogen-rich gas through the steam reforming of acetic acid using bentonite-supported catalysts was investigated. Bentonite was treated by washing and calcination. Bentonite-supported Ni, Ca, La, Ni–La, and Ni–Ca catalysts with different active metal loadings of 10 and 30 wt% were synthesized using the wet impregnation method. The catalysts were characterized using XRD, XRF, SEM, EDS, BET, FT-IR, NH3-TPD, and Raman. The activity tests of the catalysts were carried out in a continuous flow tubular reactor at various temperatures (500, 600, 700, and 800 °C). Product gas composition was determined by gas chromatography (μ-GC). The effect of bentonite treatment, active metal type, and bimetallic combinations (Ni/Bent, Ni/Bent*, La/Bent, Ca/Bent, Ni–La/Bent, and Ni–Ca/Bent) were studied. The highest hydrogen yield obtained without a catalyst was 8.61% at 700 °C. This yield increased to 74.5% at 600 °C with 30 wt% Ni–La/Bentonite, and to 42.6% with 30 wt% Ni/Bentonite catalysts, respectively. The experimental results show that bentonite has a suitable catalytic activity on its own and is a promising support material for the steam reforming of acetic acid.

Difference and similarity of coke from thermal decomposition or steam reforming of acetic acid

Polymerization/cracking and the reaction of intermediates with steam are the main routes by which the coke of very different properties might formed in steam reforming of acetic acid. This was investigated herein by conducting the steam reforming and decomposition of acetic acid on Ni/SBA-15 at 400, 550 and 700 °C, with particular focus on investigating the nature of resulting coke. Decomposition generated more coke than steam reforming at 400 °C (79.1% versus 24.6%), 550 °C (73.0% versus 45.6%) or 700 °C (39.0% versus 6.8%). More carbonaceous species like *CHx and *CC were the main intermediates, precursors of aromatic coke in decomposition, and their concentration on the catalyst surface let to serious coking at 550 °C, however, in steam reforming, oxygen-containing species like CO or C-O-C where the main intermediates precursors of coke. While larger outer diameter of carbon nanotube was formed in the reaction at 550 °C, smooth surface was formed at 700 °C.

H2O2 as an oxidizing agent to suppress coking in steam reforming of acetic acid

Coke formation and associated catalyst deactivation is a bottle-neck issue in steam reforming of most organics. Except catalyst development, introducing oxidizing agent to gasify coke or precursors of coke in steam reforming is an alternative solution. Herein, instead of using air for oxidization, hydrogen peroxide (H2O2) was used for oxidizing coke formed in steam reforming of acetic acid over Ni/SBA-15 catalyst. The rationale was that H2O2 did not dilute the hydrogen stream, due to decomposition of H2O2 to only O2 for oxidization and H2O for reforming. The results showed that the oxidization reactions induced by H2O2 formed more CO2 and CO but slightly decreased H2 production. The in-situ IR measurement of steam reforming confirmed formation of more carbonyl-containing intermediates with H2O2 presence, which were easier to be further gasified via oxidization. This resulted in substantial decrease of coking (19.5 % (percentage in spent catalyst) versus 42.4 % in steam reforming without H2O2). Furthermore, H2O2 mainly oxidized aliphatic structures in nascent coke formed, forming mainly catalytic coke of highly aromatic nature, higher thermal stability, higher resistivity towards oxidization, higher crystallinity, higher hydrophobicity, but lower ratios of olefinic C = C to aromatic C = C. Furthermore, oxidization reactions led to the coke in form of carbon nanotubes with rough surfaces and irregular structures. Moreover, H2O2 also induced a cycle of oxidization-reduction of metallic nickel in Ni/SBA-15 in the reforming.

Catalytic Performances of Ni-containing Mesoporous TUD-1 Catalysts in Steam Reforming of Acetic Acid

Catalytic Performances of Ni-containing Mesoporous TUD-1 Catalysts in Steam Reforming of Acetic Acid

Hydrogen-rich syngas production via steam reforming of acetic acid as bio-oil model compound: Effect of CaO addition to NiAl2O4 catalyst

Bio-oil by-products are inevitable with biomass gasification. It is considered a potential resource for hydrogen production via steam reforming. This study investigated acetic acid as a bio-model compound using a NiAl2O4 catalyst. The effect of reaction conditions on hydrogen-rich production has also been discussed, including reaction time (1 h, 3 h, 5 h and 7 h), steam/carbon ratio (S/C = 1–4) and the blend of NiAl2O4 and CaO (1:0, 3:1, 1:1, 1:3 and 0:1). The fresh and spent samples were characterized by XRD, XPS, SEM, BET, etc. The result showed that the CaO addition has several advantages: 1) it increases hydrogen gas purification; 2) it prevents Ni separation from NiAl2O4; 3) it decreases the sintering of NiAl2O4. However, Ca5Al6O14 formation decreases the activity of hydrogen production. In reaction conditions, steam is an essential factor for hydrogen gas production. The S/C ratio = 3 shows the optimum result for hydrogen gas production. Although the higher S/C ratio = 4 can maintain the adsorption activity of CaO, it causes Ni separation from NiAl2O4. The blend of NiAl2O4 and CaO is another essential factor for hydrogen gas production. Adding CaO has increased hydrogen gas production significantly. However, a little CaO in a blend ratio 3:1 does not maintain the stability of the NiAl2O4 structure. In the end, the optimum conditions are S/C ratio = 3 and blend = 1:1 at 650 °C, which produces hydrogen gas yield (2.1 mol/mol) and H2/CO (5.83).

Attapulgite-based MCM-41 zeolite supported Ni-Nb catalysts for hydrogen production by acetic acid steam reforming

Acetic acid steam reforming (AASR) was generally considered as one of the promising technologies for hydrogen production. In this work, the L-lysine-assisted attapulgite-based MCM-41 zeolite (LAMZ) was successfully synthesized by using attapulgite-derived silicon source and the LAMZ-supported Ni-Nb (xNi-yNb/LAMZ) catalysts were prepared via conventional impregnation method. The effects of LAMZ and Nb content on regulating the microstructures and properties of Ni-based catalysts were investigated by various characterizations. Results revealed that the addition of L-lysine could contribute to forming more void structures and increasing specific surface area of LAMZ support, which was beneficial for promoting the dispersion of active sites and enhancing the metal-support interaction. Additionally, Nb optimized the reduction of Ni, increased the concentration of surface-active Ni species, improved the strength of surface Lewis acid and promoted the formation of Ni-NbOx interfaces. Amongst, 5Ni-1Nb/LAMZ exhibited the highest surface Ni0 sites and Ni-NbOx interfaces, which further induces the generation of VO generation and the flow of lattice oxygen. Therefore, the 5Ni-1Nb/LAMZ catalyst presented the highest acetic acid conversion (82.1 %) and hydrogen yield (69.9 %) at reaction conditions of reaction temperature = 750 °C, S/C = 3, WHSV = 19.96 h−1, furthermore, it almost no any inactivation during 55 h of AASR. Additionally, the characterization results of spent catalysts confirmed that 5Ni-Nb/LAMZ possess high coke resistance and anti-sinter capability.

Hydrogen-rich syngas production from acetic acid as bio-oil model compound: Effect of intermediate phases (La2NiO4, La2O3 and Ni) of LaNiO3 catalyst

In biomass gasification, bio-oil is the main component of the condensable by-products. It is considered an attractive source for H2 production via steam reforming. This study conducted acetic acid as a bio-oil model compound with LaNiO3 perovskite catalyst due to its high oxygen vacancies and active sites. However, the perovskite structure of LaNiO3 catalysis can be destroyed by produced H2 gas, forming additional phases, including La2NiO4, La2O3 and Ni. The LaNiO3 and different phases were synthesized via a sol-gel method to probe its contribution and interaction with the H2 gas produced from steam reforming of acetic acid. Through 300 min of reaction in steam to carbon (S/C) ratio of 3, the results showed that reduced-LaNiO3 has stable H2 gas production, while the other phases decrease with time. In particular, CH4 is the main composition with the La2O3 phase. A series of characterization techniques, such as XRD, BET, XPS, SEM, TG, H2-TPR and (CO2 and O2)-TPD, were utilized to investigate fresh and used samples. The results showed that the LaNiO3-reduced phase has high oxygen storage capacity, oxygen mobility, oxygen vacancies and surface area, preventing coke deposition. In contrast, the LaNiO3 and La2NiO4 phases have poor coke deposition resistance.

Influence of Rh addition to transition metal-based catalysts in the oxidative steam reforming of acetic acid

In this work, the Rh-promotion to transition metal (Ni and Co) CeO2-supported catalysts has been studied for the first time on the acetic acid oxidative steam reforming. Characterization of the prepared catalysts confirmed the promoting effect of rhodium addition, allowing lower crystallite size which increases the number of available active sites to reactants, along with higher reducibility as evidenced by temperature-programmed reduction (H2-TPR). The influence of the reaction temperature on the acetic acid conversion and hydrogen yield was assessed. Co-based catalysts achieved better catalytic performance than Ni-based samples, almost complete acetic acid conversion, and hydrogen yields were close to the equilibrium values at temperatures over 500 ºC. On the other hand, tests at higher weight-hour space velocity evidenced the superior activity of Co-Rh/CeO2 sample. This sample showed good stability with almost complete acetic acid conversion after 25 h time-on-stream, decreasing only the hydrogen yield by 7% after the first 8 h along with a slight increase in the acetone yield of about 6%. This suggests that after the acetic acid ketonization, acetone steam reforming advanced to a lesser extent on the reaction mechanism because of long-term slight catalyst deactivation.

Modification of reaction intermediates formed from steam reforming of acetic acid with HZSM-5 or Mg-Al-LDH in upper-bed influences property of coke in lower-bed Ni/KIT-6

Modification of structures of precursors of coke is a method tackling coking in steam reforming. In this study, HZSM-5 or Mg-Al-LDH, with abundance of acidic sites or alkaline sites, were employed as upper-bed catalyst for tailoring structures of the intermediates derived from acetic acid before being reformed over Ni/KIT-6 in the lower bed. In-situ IR characterization of steam reforming indicated that aromatization of the reaction intermediates was promoted with HZSM-5, which formed more coke than with Ni/KIT-6 alone. However, the coke had a highly aromatic nature and other related features like higher thermal stability, crystallinity and hydrophobicity, which did not significantly influence the catalytic stability. Instead, the lower-bed Ni/KIT-6 showed a higher activity due to the modification of intermediates by HZSM-5, resulting in a higher hydrogen yield. In comparison, alkaline sites on Mg-Al-LDH catalyzed ketonization reactions and further condensation of ketones, forming abundant aliphatics bearing olefinic CC. Mg-Al-LDH presence formed less coke over Ni/KIT-6, but the highly polymeric coke, featuring with lower thermal stability, low C/H ratio and high hydrophilicity, led to fast deactivation of the Ni/KIT-6 in lower bed. However, the hydrogen yield was still improved by modifying the intermediates with upper-bed Mg-Al-LDH.

Used Ni/KIT-6 as a sacrificial catalyst for mitigating coking in lower-layer catalyst in steam reforming of acetic acid

Deactivated or coked catalyst from steam reforming may not always be treated as a solid waste, which might be potentially used as a sacrificial or protective layer of catalyst for reducing coke formation of catalyst in the lower bed in the same steam reforming process. In this study, steam reforming of acetic acid over Ni/KIT-6 at 600 °C was conducted with used Ni/KIT-6 in upper layer and freshly reduced Ni/KIT-6 in lower layer (dual-bed system). The results suggested that significantly more coke (3 to 4 times) formed on upper-layer catalyst (used or fresh catalyst) than on lower-layer fresh catalyst. The upper-layer used catalyst was more effectively than counterpart of fresh catalyst for mitigating coking in lower-layer catalysts. The in-situ IR technique suggested that carbonaceous species on the used catalyst impacted or reacted with the intermediates newly formed, generating more oxygen-containing species with functionalities like COC and CO of anhydride or ketones/aldehyde form. These oxygen-containing species could polymerize/condense and pass down to the lower bed, forming more polymeric coke of lower thermal stability. Differently, more unsaturated hydrocarbon species formed on the upper-layer fresh catalyst, making the coke of highly aromatic nature with a higher thermal stability and crystallinity. Additionally, modification of reaction intermediates with the used catalyst in upper layer also formed carbon nanotubes of irregular structures with coarse surface.

Oxidative steam reforming of acetic acid on Ni catalysts: Influence of the La promotion on mesostructured supports

In this work, the support effect and the La2O3 promotion of Ni-based catalysts on the oxidative steam reforming of acetic acid as bio-oil model compound has been studied. Ni/SBA-15 showed the worst catalytic performance with an acetic acid conversion dropping below 30% at 500 °C ascribed to active phase oxidation. In contrast, Ni supported over mesoporous CeO2 (CeO2-m) reached better catalytic performance and lower coke formation due to the higher Ni dispersion and oxygen mobility of the support. On the other hand, La2O3 promotion to SBA-15 and CeO2-m led to even higher Ni dispersion and prevented sintering during the reforming reaction. This effect resulted in an improvement in the catalytic performance for both promoted samples. As a consequence of low Ni crystallite size and high oxygen mobility, Ni/La2O3–CeO2-m reached almost complete conversion (∼96%), the highest hydrogen yield (∼53%) maintained for 5 h with the lowest coke formation (62.3 mgcoke·gcat−1·h−1).

Addition of tungsten in Co/Al2O3 to catalyse the production of hydrogen through acetic acid steam reforming

AbstractSteam reforming of bio‐oil is a promising green hydrogen production technology. Experimental and theoretical calculations have been carried out to study the performance of Co/Al2O3 catalysts doped with tungsten (1–10 wt%) for bio‐oil model compound acetic acid steam reforming. The maximum acetic acid conversion of 95.4 % and H2 yield of 93.5 % were obtained over the 15Co‐5W/Al2O3 catalyst under the optimized reaction conditions of temperature=550 °C, steam to carbon ratio=5 and the gas hourly space velocity of 15,780 h−1. The feeding capacity of the catalyst was improved by 2.3 times by the addition of 5 wt% W compared to that of the non‐W‐added Co/Al2O3 catalyst. Catalyst characterizations by BET, XRD, H2‐TPR, XPS, HRTEM, and SEM were performed. The results showed that high activities were maintained over 20 h on the 15Co‐5W/Al2O3 catalyst. A little filamentous coke was formed on the spent catalyst surface, and the agglomeration rate of active Co was relatively low. Density functional theory calculations confirmed that the adsorptions of CH3COOH and H2O on the catalyst were enhanced by the addition of W.

Mechanochemical preparation method for the fabrication of the mesoporous Ni–Al2O3 catalysts for hydrogen production via acetic acid steam reforming

Ni(x)-Al2O3 (x = 5, 7.5, 10, 12.5, 15, 17.5, and 20 wt%) catalysts were fabricated by the mechanochemical way, and the samples were used in acetic acid steam reforming. The results showed that all prepared samples have excellent features with a high BET area in the range of 185–215 m2 g−1. Based on the founding results, the reducibility degree of the studied samples was enhanced by raising the nickel content to 17.5 wt%. The activity results revealed that the catalyst with 17.5 wt% Ni showed the best performance, and the acetic acid conversion and hydrogen yield reached 93% and 35% at 450 °C over this sample, respectively. Also, the agglomeration of particles at higher calcination temperatures led to the decrease in acetic acid conversion by increasing the Tcalcination from 700 to 900 °C. Furthermore, the results demonstrated that the catalytic activity improved by a decrease in GHSV value from 24000 to 12000 ml h−1.g−1cat and an increase in the S/C molar ratio from 1:1 to 5:1. The influence of reduction temperature on the catalytic performance was also studied over the selected catalysts, and the results indicated that the sample under reduction temperature of 700 °C displayed the highest efficiency in the acetic acid steam reforming, which was related to the existence of more active sites and more acetic acid adsorption on the catalyst surface.

Preparation of Ni/SiO2 using silicon-rich-biomass as source for acetic acid steam reforming

In this paper, four kinds of silicon-rich biomass (rice husk, rice straw, peanut shell, corncob) were used as raw materials for SiO2 extraction by heat treatment method. And the extracted SiO2 was applied to prepare Ni/SiO2 catalyst for acetic acid (AcOH) steam reforming. Various characterization methods were used to analyze the purity, structure and specific surface area characteristics of SiO2 extracted from different sources. It was found that the silica prepared by acid washing and calcination (AWC) had larger specific surface area, abundant pore channels and larger pore volume. By water washing and calcination (WWC), K2O impurity would be remained in SiO2, which might dissolve SiO2 during the calcination process, generating an increase in the pore size and a decrease in the specific surface area. While the CaO impurity in SiO2 promoted the dispersion of the active components and enhanced the interaction between the active component and the carrier. A series of reforming catalysts were prepared by using the obtained SiO2 as carriers. It was found that the lifetime of catalyst from low to high was Ni/RS-SiO2 <Ni/PS-SiO2 <Ni/RH-SiO2, which was in the opposite order of K2O content. Acid washing was beneficial for the enhancement of Ni/RH-AC-SiO2 activity, and the increase of Ni/RS-AC-SiO2 stability. Among the four catalysts, the Ni/RH-AC-SiO2 catalyst exhibited the highest carbon conversion (100%) and hydrogen yield at 600 °C, which may be because that the acid washing removed the metal oxide impurity K2O. And its large specific surface area, the concentrated pore size distribution, and the suitable interactions between the support and carrier may also contribute to its high catalyst activity.

A thermodynamic equilibrium analysis of hydrogen and synthesis gas production from steam reforming of acetic acid and acetone blends as bio-oil model compounds

Thermodynamic analysis of steam reforming of blends of two model oxygenates, acetic acid and acetone, representing carboxylic acids and ketones in bio-oil is performed to investigate the effects of their potential interactions on hydrogen yield, synthesis gas composition and progress of reaction network. The results show that both acetic acid and acetone reach complete conversion at all operating conditions. Higher S/C molar ratio results in higher H2 and CO2 yields for both acetic acid and acetone. With the increase in pressure, H2 and CO yields are diminished whereas CH4 and CO2 yields are enhanced. H2 and CO2 yields increase with the decrease in acetone concentration in the feed blend. CO and CH4 production are affected adversely for acetic acid rich blends. The maximum H2 yield values are 75.54%, 78.34%, 80.09%, 81.78% and 84.17% at 700 °C for acetic acid/acetone blends of 0.0/1.0, 0.3/0.7, 0.5/0.5, 0.7/0.3 and 1.0/0.0, respectively.

Highly active Ni/CeO2 for the steam reforming of acetic acid using CTAB as surfactant template

A series of CTAB-templated Ni/Ce catalysts were synthesized by adding CTAB during the hydrothermal synthesis of ceria to improve the pore structure of catalysts. Their catalytic performance was evaluated in the steam reforming of acetic acid and the effects of CTAB concentration on the porous structures, reducibilities, morphology, and activity of catalysts were studied. The catalysts were characterized by BET, XRD, H2-TPR, XPS, HRTEM, in-situ DRIFTS, DTG, FTIR, and temperature-programmed reaction to elucidate the structure-activity relationship of the catalyst. The results showed that owing to the CTAB assistance, a high surface area of ceria could be achieved, which induced a better Ni dispersion with a smaller Ni size, strengthened the interaction between Ni and CeO2, and promoted the reducibility of Ni, obtaining higher activity and lower methane yield than Ni/Ce. Among these prepared samples, Ni/Ce–C6 showed the highest surface area and the best catalytic performance with a hydrogen yield of up to 82.5% even at a low temperature (550 °C). Owing to the stronger Ni-ceria interaction of Ni/Ce–C6, the lattice oxygen in ceria migrates easily to the Ni surface, interacts with the reaction intermediates, and thus improves the CO2/CO ratio in the products. Much more CO and CO2 and less CH4 were observed over Ni/Ce–C6 during the temperature-programmed reaction, indicating its high activity. In-situ DRFITS characterization demonstrated that the two types of catalysts had similar reaction intermediates but various adsorption and conversion abilities toward the acetic acid. More reaction intermediates were adsorbed at low temperatures and a higher conversion was obtained over Ni/Ce–C6 owing to its better Ni dispersion. The CTAB assistance inhibited the formation of amorphous carbon but facilitated the formation of graphitic carbon at ∼637 °C which did not induce catalyst deactivation.

A theoretical and experimental study on steam reforming of bio-oil over Ni/Co modified carbon-based catalysts

Carbon-based catalyst was prepared by Ni/Co modification of acid - pickling biochar from peanut shell. The chemical and structural properties of the modified catalyst were analyzed by BET, XRD, FTIR and SEM. At the same time, the catalytic properties of metal loading (4 wt%, 8 wt%, 12 wt%), temperature and S/C on steam reforming of acetic acid were studied. It was found that the acid-pickled biochar had abundant pore structure and oxygen-containing functional groups, and the specific surface area was up to 344.00 m2/g, which was mainly mesoporous structure and provided more active sites for metal particles loading. Under the conditions of 600℃, S/C = 3 and reaction time of 30 min, 8Ni/HPC showed the best catalytic capacity, with hydrogen content of 71.10% and acetic acid conversion of 88.03%. With the increase of temperature, the conversion of acetic acid increased obviously, but the selectivity of hydrogen decreased. Appropriate S/C can improve the selectivity of hydrogen, while excessive S/C will decrease the catalyst activity. Therefore, low-cost carbon supported Ni/Co have higher catalytic activity for the production of H2. The results provide a basis for the design of a new carbon-based catalyst and their application in steam reforming of bio-oil.

Modification of nickel-based catalyst with transition metals to tailor reaction intermediates and property of coke in steam reforming of acetic acid

Modification of Ni/Al2O3 with transition additives is known to affect physiochemical properties of the catalyst, while this will also inevitably impact evolution of reaction intermediates and property of coke formed in steam reforming. In this study, Ni/Al2O3 catalyst was modified with Fe, Zn, Cu or Co and the influences on formation of intermediate product and nature of coke was paid particular attention in steam reforming of acetic acid. The results indicated that iron or cobalt oxide reacted with NiO, forming NiFe2O4 and NiCo2O4, while copper or zinc oxide reacted with alumina, forming Al2CuO4 and ZnAl2O4, respectively. This weakened interaction between nickel oxide and alumina but also led to increase of nickel size, except Zn additive. Presence of Zn or Co in the catalyst enhanced adsorption of –OH or CO2, facilitating gasification of precursors of amorphous coke. The Cu additive intensifies adsorption/activation of oxygen-containing intermediates, while Fe was the opposite. The additive of Zn, Cu or Co, with exception of Fe, enhanced catalytic stability by suppressing formation of polymeric coke, although overall amount of coke was much higher. The coke formed in Zn, Cu or Co modified catalyst was mainly catalytic coke with a higher C/H ratio, higher crystallinity, higher thermal stability, higher portion of graphite structures, and nanotube-like structure of irregular inner cavity but with less impacts on catalytic stability.

Correlations of Lewis acidic sites of nickel catalysts with the properties of the coke formed in steam reforming of acetic acid

Coking is a major challenge in the reactions of steam reforming. In addition to the nature of metal species, the properties of carrier also affect coking behaviors of a reforming catalyst. In this work, we prepared nickel carried on Al2O3, SiO2 or the molecular sieves (25-H, 38-H) for assessed in steam reforming of acetic acid. The Ni/Al2O3 catalyst contained abundant Lewis acidic sites while the Ni/SiO2, Ni/38-H and Ni/25-H catalysts did not. The Lewis acidic sites in Ni/Al2O3 induced the polymerisation reactions to form the polymeric coke, which wrapped metallic nickel species and was the primary reason for deactivation of catalyst, even though the amount of coke was small. The substantial amount of coke formed over the other three catalysts did not lead to rapid catalyst deactivation. With the form of carbon nanotube or other forms was mainly the type of catalytic coke, depending on characteristic of the carrier. Comparing with the polymeric coke in the catalyst of Ni/Al2O3, the catalytic coke had a high C/H ratio, a much higher thermal stability and was more aromatic rich.