Steam reforming of toluene as model biomass tar to H2-rich syngas in a DBD plasma-catalytic system

Biomass tar is one of the most troublesome issues limiting the further development of biomass pyrolysis and gasification. In this study, a plasma enhanced catalytic steam reforming technology was applied for biomass tar removal. Toluene was selected as biomass tar surrogate. The nano-sized alumina-supported nickel and iron catalysts with different molar ratios of M/Al (M: Ni or Fe, 0:1, 1:3, 1:1, 3:1, 1:0) were prepared for catalytic steam reforming of toluene in a non-thermal plasma reactor featuring dielectric barrier discharge (DBD). The results showed that syngas was the dominant gas product of toluene decomposition. The conversion efficiency of toluene and energy efficiency using Ni-Al and Fe-Al catalysts both followed a sequence: M1Al3 > M1Al1 > M3Al1, which is in line with the BET surface area and pore volume. However, the selectivity of H₂ and CO catalysed by Ni-Al and Fe-Al catalysts follows the order of M1Al3 < M1Al1 < M3Al1. Presumably, toluene dissociation is a process composed of adsorption-reaction-desorption. The formation of syngas is supposed to proceed as a series of ionic and free radical reactions occurring preferably in the gas phase. Ni1Al3 catalyst shows the largest potential in converting biomass tar into H₂-rich syngas, with a maximum toluene conversion of 96% and a largest H₂ yield of 2.18 mol/mol-toluene. Besides, the results showed that this hybrid plasma-catalysis system was potential in anti-carbon deposition.     

Ni/Ru–Mn/Al2O3 catalysts for steam reforming of toluene as model biomass tar

The catalytic steam reforming of the major biomass tar component, toluene, was studied over two commercial Ni-based catalysts and two prepared Ru–Mn-promoted Ni-base catalysts, in the temperatures range 673–1073 K. Generally, the conversion of toluene and the H₂ content in the product gas increased with temperature. A H₂-rich gas was generated by the steam reforming of toluene, and the CO and CO₂ contents in the product gas were reduced by the reverse Boudouard reaction. A naphtha-reforming catalyst (46-5Q) exhibited better performance in the steam reforming of toluene at temperatures over 873 K than a methane-reforming catalyst (Reformax 330). Ni/Ru–Mn/Al₂O₃ catalysts showed high toluene reforming performance at temperatures over 873 K. The results indicate that the observed high stability and coking resistance may be attributed to the promotional effects of Mn on the Ni/Ru–Mn/Al₂O₃ catalyst.     

Steam reforming of model bio-oil compounds 2-butanone, 1-methoxy-2-propanol,ethyl acetate and butyraldehyde over Ni/Al2O3

Oil derived from fast pyrolysis of biomass (or bio-oil) is a candidate renewable feedstock for producing hydrogen (H₂). In this work, the steam reforming of model oxygenates present in the bio-oil aqueous fraction was studied in a fixed-bed reactor. Using Ni/Al₂O₃ catalyst, the reactions with 2-butanone, 1-methoxy-2-propanol, ethyl acetate and butyraldehyde were studied. To study the efficacy of the chosen catalyst for H₂ production, experiments were performed in the 623–773 K range using varying steam/carbon ratios in feed (15–25 mol/mol). The conversion of the various feeds was of the order: butyraldehyde > ethyl acetate > 1-methoxy-2-propanol > 2-butanone. The catalyst was characterized using SEM, XRD, TPR/TPD and TGA methods. It showed high stability for 7 h of time-on-stream.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Construction and reaction characteristics of pyrochlore-supported Ni catalysts for tar steam reforming

Tar is a common by-product during the gasification of biomass and its presence largely limits the subsequent application of syngas generated. Although biomass tar could be converted into hydrogen-rich syngas by catalytic steam reforming, the frequently adopted high-activity and low-cost Ni catalysts suffer from the problem of easy deactivation as a result of carbon deposition, and more efficient and stable catalyst needs to be developed for tar removal in biomass gasification. In the work, various Ni/pyrochlore catalysts characterized with redox properties were constructed and further modified through partial replacement of A-site in support, and their reaction characteristics in toluene steam reforming were comprehensively investigated. Results show that catalysts of Ni/La₂Ce₂ and Ni/Y₂Ce₂ have good catalytic performance due to the strong interaction between Ni and pyrochlore. Although a small amount doping of Sr in A-site is observed to decrease Ni/pyrochlore interaction, the great promotion in surface oxygen mobility make Ni/La_1.8Sr_0.2Ce₂ possess the best reactivity among all catalysts studied, and the optimum operating conditions is determined to be 650 °C and S/C = 2. Moreover, Ni/La_1.8Sr_0.2Ce₂ is found to be very stable during toluene steam reforming, which is proved to be a result of the superior capability in resisting coke formation.     

Enhancement of the quality of syngas from catalytic steam gasification of biomass by the addition of methane/model biogas

In this study, methane and model biogas were added during the catalytic steam gasification of pine to regulate the syngas composition and improve the quality of syngas. The effects of Ni/γ-Al₂O₃ catalyst, steam and methane/model biogas on H₂/CO ratio, syngas yield, carbon conversion rate and tar yield were explored. The results indicated that the addition of methane/model biogas during biomass steam gasification could increase the H₂/CO ratio to about 2. Methane/model biogas, steam and Ni/γ-Al₂O₃ catalyst significantly affected the quality of syngas. High H₂ content syngas with H₂/CO ratio of about 2, biomass carbon conversion >85% and low tar yield was achieved under the optimum condition: S/C = 1.5, α = 0.2 and using Ni/γ-Al₂O₃ catalyst. According to ANOVA, methane and catalyst were the key influencing factors of the H₂/CO ratio and syngas yield, and the tar yield mainly depended on the Ni/γ-Al₂O₃ catalyst. Biogas, as a more environmentally friendly material than methane, can also regulate the composition of syngas co-feeding with biomass.     

Renewable hydrogen production by steam reforming of butanol over multiwalled carbon nanotube-supported catalysts

The conversion of bio-oxygenates into hydrogen (H₂) via catalytic steam reforming is a green approach for H₂ generation. In the present work, butanol was chosen as renewable feedstock for producing H₂. Two catalysts supported on multiwalled carbon nanotubes, Ni/CNT and Co/CNT, were synthesized by the wetness impregnation method and used for butanol reforming. Trials were performed in a fixed-bed reactor in the 623–773 K range using S/C ratio equal to 33.3 mol/mol (here, S/C denotes steam to carbon ratio). The Ni/CNT catalyst exhibited higher reforming activity. The best catalytic performance for Ni/CNT was observed at T = 773 K. At this temperature, high values of butanol conversion (87.3%) and H₂ yield (0.75 mol/mol) were observed at W/F_A0 = 16.7 g h/mol (here, W is the catalyst mass and F_A0 is the molar flow rate of butanol at the inlet). The performance of Ni/CNT catalyst for steam reforming of synthetic bio-butanol was also investigated at T = 773 K and H₂ yield of 0.65 mol/mol was achieved.     

Kinetic investigation on butanol steam reforming over Ru/Al2O3 catalyst

Steam reforming of biomass-derived oxygenates is an attractive technique for the renewable production of hydrogen (H₂). In this work, steam reforming of n-butanol – a representative of bio-oxygenates – was studied over commercial 5% Ru/Al₂O₃ catalyst in a fixed-bed reactor. Kinetics of butanol reforming was investigated between temperatures 623 and 773 K at steam/carbon (S/C) ratio equal to 33.3 mol/mol. The W/F_A0 ratio (W: mass of catalyst, F_A0: molar flow rate of butanol in feed) was varied between 3.3 and 16.7 g h/mol. At T = 773 K, butanol conversion and H₂ yield were 93.4% and 0.61 mol/mol. Evaluation of the kinetic data showed that reaction order with respect to butanol was unity. The activation energy for the investigated reaction was 78 kJ/mol. Finally, a Langmuir-Hinshelwood model that assumed the surface reaction between the adsorbed reactants as rate-determining was used to describe the kinetic data.     

Experimental study on biomass steam gasification for hydrogen-rich gas in double-bed reactor

Based on Response Surface Methodology, the experiments of biomass catalytic gasification designed by Design-Expert software were carried out in steam atmosphere and double-bed reactor. The response surface was set up with three parameters (gasification temperature, the content of K-based catalyst in gasification bed and the content of Ni-based catalyst in reforming bed) for biomass gasification performance of carbon conversion efficiency and hydrogen yield to make analysis and optimization about the reaction characteristics and gasification conditions. Results showed that gasification temperature and the content of K-based catalyst in gasification bed had significant influence on carbon conversion efficiency and hydrogen yield, whilst the content of Ni-based catalyst in reforming bed affected the gasification reactions to a large extent. Furthermore, appropriate conditions of biomass steam gasification were 800 °C for gasification temperature, 82% for the content of K-based catalyst in gasification bed and 74% for the content of Ni-based catalyst in reforming bed by the optimization model. In these conditions, the steam gasification experiments using wheat straw showed that carbon conversion efficiency was 96.9% while hydrogen yield reached 64.5 mol/kg, which was in good agreement with the model prediction. The role of the reforming bed was also analyzed and evaluated, which provided important insight that the employment of reforming bed made carbon conversion efficiency raised by 4.8%, while hydrogen yield achieved a relative growth of 50.5%.     

Activity of Fe supported by Ce1−xSmxO2−δ derived from metal complex decomposition toward the steam reforming of toluene as biomass tar model compound

Ceria (CeO₂) and samaria doped ceria (Ce_1−xSm_xO_2−δ) powders with various Ce/Sm ratios have been successfully prepared via metal complex decomposition. The catalytic activities of these synthesized materials toward the steam reforming of toluene as model compound of biomass tar were studied with an aim to determine the suitable catalyst for biomass tar decomposition in biomass gasification system. From the study, H₂, CO, CO₂, CH₄, C₂H₄ and C₂H₆ were the main products from the reaction with low carbon deposition observed on the catalyst surface after 18 h operation. Among all catalysts, relatively higher toluene conversion and H₂ yield (32.8%) with greater resistance toward carbon deposition was achieved from Ce_0.85Sm_0.15O_2−δ. To enhance better toluene conversion and H₂ yield, Ce_0.85Sm_0.15O_2−δ was further applied as the catalyst support by impregnating low-cost Fe on its surface; and its reforming activity was compared to Ni and Fe supported over conventional γ-Al₂O₃. It was found that, Fe/Ce_0.85Sm_0.15O_2−δ offered significantly higher toluene conversion and H₂ yield than Fe/Al₂O₃ (55.2% H₂ yield compared to 16.5%). Its reforming activity was also comparable to Ni/Al₂O₃ with better H₂ yield stability after 72 h operation (16% deactivation for Fe/Ce_0.85Sm_0.15O_2−δ compared to 35% deactivation for Ni/Al₂O₃). Therefore, Fe/Ce_0.85Sm_0.15O_2−δ has good potential to replace Ni-based catalyst in biomass gasification system.     

Perovskite-based catalysts for tar removal by steam reforming: Effect of the presence of hydrogen sulfide

One of the greatest problems in biomass gasification processes is the conditioning of the produced synthesis gas, which contains various contaminants, including tar and hydrogen sulfide. Nickel catalysts, designed for steam reforming of aliphatic hydrocarbons (natural gas and nafta), are usually deactivated by coke deposition and sulfur poisoning. In this work, nickel and/or manganese catalysts derived from perovskites were prepared by the citrate method and characterized by X-ray diffraction, N₂ physisorption and temperature programmed reduction. The catalysts were evaluated in the steam reforming of toluene, used as tar model compound, in the absence of H₂S at 700 °C and in the presence of 50 ppm H₂S at 800 °C. LaNi_0.5Mn_0.5O₃ catalyst showed higher activity and stability in the absence of H₂S. LaMnO₃ catalyst, although less active in the absence of H₂S, showed increased stability in the presence of H₂S, with conversion of about 60%. H₂ production was only observed in the absence of H₂S.     

Steam reforming of toluene as a tar model compound with modified nickel-based catalyst

Catalytic steam reforming is a promising route for tar conversion to high energy syngas in the process of biomass gasification. However, the catalyst deactivation caused by the deposition of residual carbon is still a major challenge. In this paper, a modified Ni-based Ni-Co/Al₂O₃-CaO (Ni-Co/AC) catalyst and a conventional Ni/Al₂O₃ (Ni/A) catalyst were prepared and tested for tar catalytic removal in which toluene was selected as the model component. Experiments were conducted to reveal the influences of the reaction temperature and the ratio between steam to carbon on the toluene conversion and the hydrogen yield. The physicochemical properties of the modified Ni-based catalyst were determined by a series of characterization methods. The results indicated that the Ni-Co alloy was determined over the Ni-Co/AC catalyst. The doping of CaO and the presence of Ni-Co alloy promoted the performance of toluene catalytic dissociation over Ni-Co/AC catalyst compared with that over Ni/A catalyst. After testing in steam for 40 h, the carbon conversion over Ni-Co/AC maintained above 86% and its resistance to carbon deposition was superior to Ni/A catalyst.     

Steam reforming of ethanol on Rh/SiCeO2 washcoated monolith catalyst: Stable catalyst performance

The performance of a new Rh/CeSiO₂ catalyst supported on a ceramic monolith for steam reforming (SR) of ethanol for hydrogen generation was investigated. It provides several advantages over a traditional pellet based catalyst in that it will reduce weight, size and pressure drop in the reactor. The effect of steam to ethanol molar ratio and temperature were first investigated on a powdered catalyst in order to establish the preferred reaction conditions to be used for tests on the monolith. The optimum temperature for coke free, high selectivity and stable catalyst operation was 1073 K at a steam to ethanol molar ratio of 3.5. The monolith supported catalyst was evaluated for aging stability, on/off performance and coke regeneration using steam gasification. After 96 h of SR of ethanol at 1028 K and water/ethanol molar ratio of 3.5 the monolith supported catalyst retained stable performance throughout the entire time on stream with the only products being H₂, CO, CO₂. Some coke formation was observed using Raman spectra, however, it did not cause any permanent deactivation. Regeneration via steam gasification at 973 K with 20% steam in N₂ was successful for coke removal and complete catalyst regeneration.     

Promotional effects of Ce on NiCe/γAl2O3 for enhancement of H2 in hydrothermal gasification of biomass

This communication presents promotional effects of Ce on a NiCe/γ-Al₂O₃ catalyst for biomass gasification in hydrothermal reaction conditions. The catalyst samples were prepared by an incipient wetness technique using a successive metal loading approach. The TPR/TPO results showed that the presence of Ce minimized metal support interaction and improved the reducibility and thermal stability of the catalyst. The XRD analysis of fresh and reduced (after 10 repeated TPR/TPO cycles) catalyst samples showed unchanged crystal structures of the nickel particles indicating stable properties of the NiCe/γAl₂O₃ catalyst. The hydrothermal biomass gasification experiments were conducted using glucose as a biomass surrogate at various reaction temperature (425–525 °C) and time (5–35 min), while the pressure was maintained at 25.5 MPa. It was observed that the addition of Ce influenced the catalyst surface creating more active nickel sites for steam reforming methane reaction. Ce also increased the activity of Ni/γAl₂O₃ catalysts in terms of hydrogen production by promoting the water gas shift reaction and suppressing the methanation reaction of carbon dioxide.     

Hydrotalcites with vanadium,effective catalysts for steam reforming of toluene

The steam reforming of toluene has been studied on three catalysts with vanadium (0.9, 1.75, 3%) derived from hydrotalcites precursors (Mg/Al molar ratio 3) in the temperature range 400–500 °C. Catalysts were characterized by BET, XRD, SEM, TEM, FT-IR and then a correlation between physico-chemical characteristics and catalytic activity for toluene steam reforming has been done. The results showed that the catalyst with 3% V, with polyvanadate species, achieves the best catalytic activity, with a toluene conversion of 77.5%, at 500 °C, and a H₂ composition of 57%.     

Steam reforming of acetic acid for hydrogenproduction: Catalytic performances of Ni and Co supported on Ce0·75Zr0·25O2 catalysts

The catalytic steam reforming of acetic acid over both Ni/ and Co/Ce_0·75Zr_0·25O₂ (CZO) catalysts in the temperature range of 450–650 °C and steam-to-carbon molar ratios of 3–9 was studied. It was found that the complete acetic acid conversion was achieved for all the conditions investigated. Nevertheless, the C–C bond cleavage conversion was attained less than the acetic acid conversion at a given condition due to carbon deposition on the catalyst. However, hydrogen yield was obtained in the same trend as C–C bond cleavage conversion as well. The results revealed that the CZO as an active support prefers to promote the ketonization reaction to the C-C bond cleavage reaction at a lower temperature, and vice versa at a higher temperature. The Ni/CZO catalyst exhibits higher C–C bond cleavage conversion than the Co/CZO catalyst particularly at 650 °C whereas the Co/CZO catalyst is more active for ketonization reaction at low temperatures. However, as an increase in reaction temperature, the Co/CZO catalyst promotes ketonization reaction more pronouncedly toward aldol-condensation reaction thus giving rise to the carbon deposition. The results deduced from the effect of space velocity on the activity and product distribution suggested that the steam reforming of acetic acid over Ni/CZO catalyst is dominated by decomposition of acetic acid, while that of Co/CZO catalyst by ketonization reaction.     

Effect of pollutants on biogas steam reforming

This study reports the influence of biogas poisoning on a Ni based catalyst working under steam reforming conditions (atmospheric pressure, T = 1073 K and H₂O/CH₄ = 2 mol/mol). A biogas stream composed by CH₄ and CO₂ with a ratio 55/45 vol.%, added with different chemical species (H₂S, hydrocarbons mixture and D5) as contaminants, was used as inlet gas stream.First, effect of poisoning on Ni catalyst were separately evaluated and the boundary concentrations for each contaminants were revealed (0.4 ppm, 200 ppm and 0.5 ppm for H₂S, hydrocarbons and D5 respectively) to assure Ni stable performances on time on stream (100 h at 50,000 h^?1 of GHSV). Successively, a comparison between Ni catalytic behaviors in presence of two combined poisoning in the biogas (H₂S + Hydrocarbons and Hydrocarbons + D5) was carried out.It was found that the effect of combined poisoning, even though it considered in moderate concentration, is harmful for Ni catalyst activity. Methane conversion on time on stream was reduced from 86% to 40% after 50 h, when the couple of poisoning Hydrocarbons + D5 was added to the inlet gas stream, while a lower deactivation pattern (about 73%) was leaded by couple H₂S + Hydrocarbons. Both poisoning mixtures promoted coke deposition on Ni catalyst surface (about ≥0.5 mgC/g_cat·h) independently by poisoning chemical characteristics probably due to adsorption/deposition of contaminants on catalytic sites.     

Performance of active nickel loaded lignite char catalyst on conversion of coffee residue into rich-synthesis gas by gasification

Performance of nickel-loaded lignite char catalyst on conversion of coffee residue into synthesis gas by catalytic steam gasification was carried out at low reaction temperatures ranging from 500 °C to 650 °C in the two-stage quartz fixed bed reactor. The effects of steam pressures (30, 36 and 50 kPa corresponding to S/B = 2.23, 2.92 5.16, respectively) and catalyst to biomass ratios (C/B ratio = 0, 1, 3) were considered. Nickel-loaded lignite char was prepared as a catalyst with a low nickel loading amount of 12.9 wt%. The gas yields in the catalytic steam gasification process strongly depended on the reaction temperature and C/B ratio. The total gas yields obtained in catalytic steam gasification was higher than that of catalytic pyrolysis, steam gasification and non-catalytic pyrolysis with steam absence by factors of 3.0, 3.8 and 7.7, respectively. To produce the high synthesis gas, it could be taken at 600 °C with total gas yields of 67.13 and 127.18 mmol/g biomass-d.a.f. for C/B ratios of 1.0 and 3.0, respectively. However, the maximum H₂/CO ratio was 3.57 at a reaction temperature of 600 °C, S/B of 2.23 and C/B of 1.0. Considering the conversion of coffee residue by catalytic steam gasification using the nickel-loaded lignite char catalyst, it is possible to covert the coffee residue volatiles into rich synthesis gas.     

Ni-CeO2/SBA-15电催化甲苯水蒸气重整的实验研究

以甲苯为生物质气化焦油的模型化合物,以Ni-CeO₂/SBA-15为催化剂,在自行搭建的固定床电化学催化（电催化）水蒸气重整实验台上进行了甲苯的电催化水蒸气重整实验,考察了电流强度、反应温度和水/碳摩尔比（S/C）对甲苯转化率、产气组成的影响,并对该催化剂进行了长时间活性测试。结果表明,电流的引入可以显著提高催化剂对甲苯的转化效率;在电流为4 A、反应温度为800℃、S/C为3时,甲苯转化率可以达到94.7%。     

Kinetic study of the catalytic reforming of biomass pyrolysis volatiles over a commercial Ni/Al2O3 catalyst

An original kinetic model has been proposed for the reforming of the volatiles derived from biomass fast pyrolysis over a commercial Ni/Al₂O₃ catalyst. The pyrolysis-reforming strategy consists of two in-line steps. The pyrolysis step is performed in a conical spouted bed reactor (CSBR) at 500 °C, and the catalytic steam reforming of the volatiles has been carried out in-line in a fluidized bed reactor. The reforming conditions are as follows: 600, 650 and 700 °C; catalyst mass, 0, 1.6, 3.1, 6.3, 9.4 and 12.5 g; steam/biomass ratio, 4, and; time on stream, up to 120 min. The integration of the kinetic equations has been carried out using a code developed in Matlab. The reaction scheme takes into account the individual steps of steam reforming of bio-oil oxygenated compounds, CH₄ and C₂-C₄ hydrocarbons, and the WGS reaction. Moreover, a kinetic equation for deactivation has been derived, in which the bio-oil oxygenated compounds have been considered as the main coke precursors. The kinetic model allows quantifying the effect reforming conditions (temperature, catalyst mass and time on stream) have on product distribution.