Renewable hydrogen generation by steam reforming of glycerol over zirconia promoted ceria supported catalyst

The study focuses on hydrogen production from steam reforming of glycerol over nickel based catalyst promoted by zirconia and supported over ceria. Catalyst was prepared by the wet-impregnation method and characterized by BET surface area analysis, X-ray diffraction technique and scanning electron microscopy (SEM) analysis. The performance of the catalyst was evaluated in terms of hydrogen yield, selectivity and glycerol conversion at 700 °C in a tubular fixed bed reactor. The effect of glycerol concentration in feed, space time (W/F_AO), temperature and time on stream (TOS) was analyzed for the catalyst Ni–ZrO₂/CeO₂ which showed the complete conversion of glycerol and high H₂ yield that corresponds to 3.95 mol of H₂ out of 7 mol. Thermodynamic analysis was also carried out using Aspen HYSYS for system having glycerol concentration 10 wt% and 20 wt% and experimental results were compared with thermodynamics. Kinetic study was carried out for the steam reforming of glycerol over Ni–ZrO₂/CeO₂ catalyst using the power law model. The values of activation energy and order of reaction were found to be 43.4 kJ/mol and 0.3 respectively.     

Ultrasonic-assisted synthesis of highly active catalyst Au/MnOx–CeO2 used for the preferential oxidation of CO in H2-rich stream

A series of nano-gold catalysts supported on binary oxides MO_x–CeO₂ (atomic ratio M/Ce = 1:1, M = Mn, Fe, Co, Ni) are prepared by deposition–precipitation (DP). An innovative and rather convenient ultrasonic pretreatment of the support is employed for Au/MnO_x–CeO₂ preparation. It is found that for preferential CO oxidation Au/MnO_x–CeO₂ is more active than Au/CeO₂. Ultrasonic pretreatment of MnO_x–CeO₂ further promotes the performance of Au/MnO_x–CeO₂, with CO conversion increased by 24 % at 120 °C. Meanwhile, the selectivity of oxygen to CO₂ is promoted in the whole temperature range, especially in 80–120 °C, the selectivity is increased by 15–21%. HR-TEM and XRD results indicate that ultrasonic pretreatment is favorable to the formation of much smaller gold nanoparticles (<5 nm). The characterization of XPS, UV–vis DRS, H₂-TPR and CO-TPR confirms that the strong interaction between Au and the support effectively inhibits the dissociation and oxidation of H₂ over the ultrasonically pretreated catalyst Au/MnO_x–CeO₂, making it highly selective to CO oxidation.     

Hydrogen production by low-temperature reforming of organic compounds in bio-oil over a CNT-promoting Ni catalyst

Present study reports on high catalytic activity of CNTs-supported Ni catalyst (x% Ni-CNTs) synthesized by the homogeneous deposition–precipitation method, which was successfully applied for low-temperature reforming of organic compounds in bio-oil. The optimal Ni-loading content was about 15 wt%. The H₂ yield over the 15 wt% Ni-CNTs catalyst reached about 92.5% at 550 °C. The influences of the reforming temperature (T), the molar ratio of steam to carbon fed (S/C) and the current (I) passing through the catalyst, on the reforming process of the bio-oil over the Ni-CNTs' catalysts were investigated using the stream as the carrier gas in the reforming reactor. The features of the Ni-CNTs' catalysts with different loading contents of Ni were investigated via XRD, XPS, TEM, ICP/AES, H₂-TPD and the N₂ adsorption–desorption isotherms. From these analyses, it was found that the uniform and narrow distribution with smaller Ni particle size as well as higher Ni dispersion was realized for the CNTs-supported Ni catalyst, leading to excellent low-temperature reforming of oxygenated organic compounds in bio-oil.     

Direct ethanol fuel cells based on PtSn anodes: the effect of Sn content on the fuel cell performance

In the present work, several carbon supported PtSn catalysts with different Pt/Sn atomic ratios were synthesized and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Both the results of TEM and XRD showed that all in-house prepared carbon supported Pt and PtSn catalysts had nanosized particles with narrow size distribution. According to the primary analysis of XPS results, it was confirmed that the main part of Pt of the as-prepared catalysts is in metallic state while the main part of Sn is in oxidized state. The performances of single direct ethanol fuel cells were different from each other with different anode catalysts and at different temperatures. It was found that, the single DEFC employing Pt₃Sn₂/C showed better performance at 60 °C while the direct ethanol fuel cells with Pt₂Sn₁/C and Pt₃Sn₂/C exhibited similar performances at 75 °C. Furthermore, at 90 °C, Pt₂Sn₁/C was identified as a more suitable anode catalyst for direct ethanol fuel cells in terms of the fuel cell maximum power density. Surface oxygen-containing species, lattice parameters and ohmic effects, which are related to the Sn content, are thought as the main factors influencing the catalyst activity and consequently the performance of single direct ethanol fuel cells.     

Investigation of ethanol electrooxidation on a Pt–Ru–Ni/C catalyst for a direct ethanol fuel cell

This research is aimed to improve the utilization and activity of anodic alloy catalysts and thus to lower the contents of noble metals and the catalyst loading on anodes for ethanol electrooxidation. The DEFC anodic catalysts, Pt–Ru–Ni/C and Pt–Ru/C, were prepared by a chemical reduction method. Their performances were tested by using a glassy carbon working electrode and cyclic voltammetric curves, chronoamperometric curves and half cell measurement in a solution of 0.5 mol L⁻¹ CH₃CH₂OH and 0.5 mol L⁻¹ H₂SO₄. The composition of the Pt–Ru–Ni and Pt–Ru surface particles were determined by EDAX analysis. The particle size and lattice parameter of the catalysts were determined by means of X-ray diffraction (XRD). XRD analysis showed that both of the catalysts exhibited face centered cubic structures and had smaller lattice parameters than a Pt-alone catalyst. Their particle sizes were small, about 4.5 nm. No significant differences in the ethanol electrooxidation on both electrodes were found using cyclic voltammetry, especially regarding the onset potential for ethanol electrooxidation. The electrochemically active specific areas of the Pt–Ru–Ni/C and Pt–Ru/C catalysts were almost the same. But, the catalytic activity of the Pt–Ru–Ni/C catalyst was higher for ethanol electrooxidation than that of the Pt–Ru/C catalyst. Their tolerance to CO formed as one of the intermediates of ethanol electrooxidation, was better than that of the Pt–Ru/C catalyst.     

Hydrogen production by oxidative reforming of ethanol in a fluidized bed reactor using a PtNi/CeO2SiO2 catalyst

Oxidative steam reforming of ethanol (OESR) was investigated over PtNi/CeO₂SiO₂ catalysts prepared from different cerium salt precursors. During stability tests performed at 500 °C, steam/ethanol ratio (S/E) of 4 and oxygen/ethanol ratio of 0.5 (O/E), the highest performance was recorded over the catalyst prepared form organic precursors. The most promising formulation was tested at different temperatures, S/E and O/E. Complete conversion was recorded during 100 h of the test at 600 °C, with a very low carbon formation rate (6.9·10⁻⁷ g_{coke, oxidized}·g_catalyst⁻¹·g_carbon,fed⁻¹·h⁻¹). The increase of oxygen content in the reacting mixture from 5 to 7.5% had a beneficial effect on H₂ yield, which rose of more than 20% after 100 h of test, and on the conversion of by-products. When steam/ethanol ratio grew from 4 to 6, a slightly lower performance improvement was observed. Therefore, the highest activity and stability during OESR over the PtNi/CeO₂SiO₂ catalyst prepared from organic salts was achieved at 600 °C, O/E = 0.75 and S/E = 6.     

Glycine-assisted preparation of highly dispersed Ni/SiO2 catalyst for low-temperature dry reforming of methane

Ni-based catalysts have been widely studied in reforming methane with carbon dioxide. However, Ni-based catalysts tends to form carbon deposition at low temperatures (≤600 °C), compared with high temperatures. In this paper, a series of Ni/SiO₂-XG catalysts were prepared by the glycine-assisted incipient wetness impregnation method, in which X means the molar ratio of glycine to nitrate. XRD, H₂-TPR, TEM and XPS results confirmed that the addition of glycine can increase Ni dispersion and enhance the metal-support interaction. When X ≥ 0.3, these catalysts have strong metal-support interaction and small Ni particle size. The Ni/SiO₂-0.7G catalyst has the best catalytic performance in dry reforming of methane (DRM) test at 600 °C, and its CH₄ conversion is 3.7 times that of Ni/SiO₂-0G catalyst. After 20 h reaction under high GHSV (6 × 10⁵ ml/g_cat/h), the carbon deposition of Ni/SiO₂-0.7G catalyst is obviously lower than that of Ni/SiO₂-0G catalyst. Glycine-assisted impregnation method can enhance the metal-support interaction and decrease the metal particle size，which is a method to prepare highly dispersed and stable Ni-based catalyst.     

Reactivity of pulverized coals during combustion catalyzed by CeO2 and Fe2O3

Effects of CeO₂ and Fe₂O₃ on combustion reactivity of several fuels, including three ranks of coals, graphite and anthracite chars, were investigated using thermo-gravimetric analyzer. The results indicated that the combustion reactivity of all the samples except lignite was improved with CeO₂ or Fe₂O₃ addition. It was interesting to note that the ignition temperatures of anthracite were decreased by 50 °C and 53 °C, respectively, with CeO₂ and Fe₂O₃ addition and that its combustion rates were increased to 15.4%/min and 12.2%/min. Ignition temperatures of lignite with CeO₂ and Fe₂O₃ addition were 250 °C and 226 °C, and the combustion rates were 12.8% and 19.3%/min, respectively. When compared with those of lignite without catalysts, no obvious catalytic effects of the two catalysts on its combustion reactivity were revealed. The results from the combustion of the three rank pulverized coals catalyzed by CeO₂ and Fe₂O₃ indicated significant effects of the two catalysts on fixed carbon combustion. And it was found that the higher the fuel rank, the better the catalytic effect. The results of combustion from two kinds of anthracite chars showed obvious effects of anthracite pyrolysis catalyzed by CeO₂ and Fe₂O₃ on its combustion reactivity.     

Ethanol oxidative steam reforming over Ni-based catalysts

Oxidative steam reforming of ethanol for hydrogen production in order to feed a solid polymer fuel cell (SPFC) has been studied over several catalysts at on board conditions (a molar ratio of H₂O/EtOH and of O₂/EtOH equal to 1.6 and 0.68 respectively) and a reforming temperature between 923 and 1073 K. Two Ni (11 and 20 wt.%)/Al₂O₃ catalysts and five bimetallic catalysts, all of them supported on Al₂O₃, were tested. The bimetallic catalysts were Ni (approximately 20 wt.%) based catalysts doped with Cr (0.65 wt.%), Fe (0.6 wt.%), Zn (0.7 wt.%) or Cu (0.6 and 3.1 wt.%). The results in terms of H₂ production and CO₂/CO_x ratio obtained over Ni-based catalysts supported on Al₂O₃ are compared with those obtained over Ni–Cu/SiO₂ and Rh/Al₂O₃ catalysts reported in our previous works. Tendencies of the product selectivities are analyzed in the light of the reaction network proposed.     

Cu,Mg and Co effect on nickel-ceria supported catalysts for ethanol steam reforming reaction

Ethanol steam reforming is a promising reaction which produces hydrogen from bio and synthetic ethanol. In this study, the nano-structured Ni-based bimetallic supported catalysts containing Cu, Co and Mg were synthesized through impregnation method and characterized by XRD, BET, SEM, TPR and TPD analysis. The prepared catalysts were tested in steam reforming of ethanol in the S/C = 6, GHSV of 20,000 mL/(g_cat h) at the temperature range of 450–600 °C. Among the xNi/CeO₂ (x = 10, 13, 15 wt%) catalyst, the sample containing 13 wt% Ni with surface area of 64 m²/g showed the best performance with 89% ethanol conversion and 71% H₂ selectivity as well as low CO selectivity of 8% at 600 °C and The addition of Cu, Mg, and Co to catalyst structure were evaluated and it was found that the nature of second metal has a strong influence on the catalyst selectivity for H₂ production. Considering to results of TPR analysis, the 13Ni–4Cu/CeO₂ catalyst showed proper reduction which caused in better activity. On the other side based on TPD analysis, the more basic property of 13Ni–4Mg/CeO₂ bimetallic catalyst provided a better condition to methane steam reforming, leading to lower CH₄ selectivity and consequently more H₂ production. The 13Ni–4Cu/CeO₂ exhibited the highest activity and lowest selectivity towards ethanol conversion and CO production about 99% and 4%, while the 13Ni–4Mg/CeO₂ catalyst possessed the highest H₂ selectivity and lowest CH₄ selectivity about 74% and 1% respectively at 600 °C. The Ni–Cu and Ni–Mg bimetallic catalysts shows good stability with time on stream.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/Al2O3–ZrO2 xerogel catalysts: Effect of calcination temperature of Al2O3–ZrO2 xerogel supports

Al₂O₃–ZrO₂ (AZ) xerogel supports prepared by a sol-gel method were calcined at various temperatures. Ni/Al₂O₃–ZrO₂ (Ni/AZ) catalysts were then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AZ supports on the catalytic performance of Ni/AZ catalysts in the steam reforming of LNG was investigated. Crystalline phase of AZ supports was transformed in the sequence of amorphous γ-Al₂O₃ and amorphous ZrO₂ → θ-Al₂O₃ and tetragonal ZrO₂ → (θ + α)-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ → α-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ with increasing calcination temperature from 700 to 1300 °C. Nickel oxide species were strongly bound to γ-Al₂O₃ and θ-Al₂O₃ in the Ni/AZ catalysts through the formation of solid solution. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AZ supports. Nickel surface area of Ni/AZ catalysts was well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni/AZ1000 (nickel catalyst supported on AZ support that had been calcined at 1000 °C) with the highest nickel surface area showed the best catalytic performance. Well-developed and pure tetragonal phase of ZrO₂ in the AZ1000 support played an important role in the adsorption of steam and the subsequent spillover of steam from the support to the active nickel.     

Effect of temperature on the mechanism of ethanol oxidation on carbon supported Pt,PtRu and Pt3Sn electrocatalysts

The electrochemical oxidation of ethanol on carbon supported Pt, PtRu and Pt₃Sn catalysts was studied in acid solutions at room temperature and in direct ethanol fuel cells (DEFC) in the temperature range 70–100 °C. In all the experiments, an enhancement of the activity for the ethanol oxidation was observed on the binary catalysts. In acid solution the improvement at low current densities was higher on PtRu than on Pt₃Sn. In DEFC tests, at 70 °C the cells with PtRu and Pt₃Sn showed about the same performance, while for T > 70 °C the cells with Pt₃Sn as anode material performed better than those with PtRu as anode material. The apparent activation energy for ethanol oxidation on PtRu catalyst was lower than on Pt₃Sn, particularly at high cell potentials, i.e. at low current densities. At low temperatures and/or low current densities, the positive effect of Ru oxides on the bifunctional mechanism determined the enhancement of activity for the ethanol oxidation reaction, while at high temperatures the positive effect of Sn alloying (enlarged lattice parameter) on CH₃CH₂OH adsorption and C–C cleavage prevails.     

Low-temperature catalytic conversion of greenhouse gases (CO2 and CH4) to syngas over ceria-magnesia mixed oxide supported nickel catalysts

Running dry reforming of methane (DRM) reaction at low-temperature is highly regarded to increase thermal efficiency. However, the process requires a robust catalyst that has a strong ability to activate both CH₄ and CO₂ as well as strong resistance against deactivation at the reaction conditions. Thus, this paper examines the prospect of DRM reaction at low temperature (400–600 °C) over CeO₂–MgO supported Nickel (Ni/CeO₂–MgO) catalysts. The catalysts were synthesized and characterized by XRD, N₂ adsorption/desorption, FE-SEM, H₂-TPR, and TPD-CO₂ methods. The results revealed that Ni/CeO₂–MgO catalysts possess suitable BET specific surface, pore volume, reducibility and basic sites, typical of heterogeneous catalysts required for DRM reaction. Remarkably, the activity of the catalysts at lower temperature reaction indicates the workability of the catalysts to activate both CH₄ and CO₂ at 400 °C. Increasing Ni loading and reaction temperature has gradually increased CH₄ conversion. 20 wt% Ni/CeO₂–MgO catalyst, CH₄ conversion reached 17% at 400 °C while at 900 °C it was 97.6% with considerable stability during the time on stream. Whereas, CO₂ conversions were 18.4% and 98.9% at 400 °C and 900 °C, respectively. Additionally, a higher CO₂ conversion was obtained over the catalysts with 15 wt% Ni content when the temperature was higher than 600 °C. This is because of the balance between a high number of Ni active sites and high basicity. The characterization of the used catalyst by TGA, FE-SEM and Raman Spectroscopy confirmed the presence of amorphous carbon at lower temperature reaction and carbon nanotubes at higher temperature.     

From wood wastes to hydrogen – Preparation and catalytic steam reforming of crude bio-ethanol obtained from fir wood

Fir wood wastes were used to produce crude bio-ethanol by two methods: simultaneous saccharification and fermentation (SSF) and acid hydrolysis followed by the fermentation of the acid hydrolyzate. The main components of crude bio-ethanol are ethanol and acetic acid. In addition, low concentrations of a wide range of alcohols, acids, esters, ethers and aldehydes are also present. Ethanol concentration is higher in the SSF process than in the acid hydrolysis: 43.69 g/L compared to 37.53 g/L, respectively. Opposite to ethanol concentration, the acetic acid concentration is higher in the acid hydrolysis process: 16.36 g/L compared to 10.24 g/L, respectively. The crude bio-ethanol was used to produce hydrogen by catalytic steam reforming. The tested catalysts were the common Ni/Al₂O₃ and two rare earth oxides promoted Ni catalysts: Ni/La₂O₃–Al₂O₃ and Ni/CeO₂–Al₂O₃ prepared by successive wet impregnation. The characterization techniques revealed that the addition of rare earth oxides improves the Ni dispersion and the reducibility of the promoted catalysts. The best feed rate which assures the optimal ratio between conversion and catalyst deactivation is 0.8 mL/min bio-ethanol. The addition of extra oxide (La₂O₃ and CeO₂) to the support improves the ethanol conversion especially at 250 °C, but no significant effect on the acetic acid conversion was observed. At 250 °C the ethanol conversion is almost 90% for Ni/La₂O₃–Al₂O₃ and Ni/CeO₂–Al₂O₃, but the acetic acid conversion is below 30% for all catalysts. At 350 °C both ethanol and acetic acid present maximum conversion. At this temperature the best hydrogen production is obtained for Ni/La₂O₃–Al₂O₃ due to better ethanol conversion and better selectivity for hydrogen formation. At 350 °C the promoted catalysts are stable for 4 h time on stream, different degrees of deactivation being obtained at lower temperatures.     

Study of Ni/CeO2–ZnO catalysts in the production of H2 from acetone steam reforming

This paper reports the study of new Ni/ZnO-based catalysts for hydrogen production from substoichiometric acetone steam reforming (ASR). The effect of CeO₂ introduction is analyzed regarding the catalytic behavior and carbon deposits formation. ASR was studied at 600 °C using a steam/carbon ratio S/C = 1. Ni/xCeZnO (x = 10, 20, 30 CeO₂ wt %) catalysts showed a better performance than the bare Ni/ZnO. Ni/xCeZnO generated a lower amount and less ordered carbon deposits than Ni/ZnO. The higher the CeO₂ content in Ni/xCeZnO, the lower the amount of carbon deposits in the post-reaction catalyst. The highest H₂ production under ASR at the experimental conditions used was achieved for the Ni/xCeZnO catalysts. In-situ DRIFTS-MS experiments under ESR conditions showed different reaction pathways over Ni/20CeZnO and Ni/ZnO catalysts.     

Optimization of ethanol production from sweet sorghum (Sorghum bicolor) juice using response surface methodology

Sweet sorghum juice was fermented into ethanol using Saccharomyces cerevisiae (ATCC 24858). Factorial experimental design, regression analysis and response surface method were used to analyze the effects of the process parameters including juice solid concentration from 6.5 to 26% (by mass), yeast load from 0.5 g L⁻¹ to 2 g L⁻¹ and fermentation temperature from 30 °C to 40 °C on the ethanol yield, final ethanol concentration and fermentation kinetics. The fermentation temperature, which had no significant effect on the ethanol yield and final ethanol concentration, could be set at 35 °C to achieve the maximum fermentation rate. The yeast load, which had no significant effect on the final ethanol concentration and fermentation rate, could be set at 1 g L⁻¹ to achieve the maximum ethanol yield. The juice solid concentration had significant inverse effects on the ethanol yield and final ethanol concentration but a slight effect on the fermentation rate. The raw juice at a solid concentration of 13% (by mass) could be directly used during fermentation. At the fermentation temperature of 35 °C, yeast solid concentration of 1 g L⁻¹ and juice solid concentration of 13%, the predicted ethanol yield was 101.1% and the predicted final ethanol concentration was 49.48 g L⁻¹ after 72 h fermentation. Under this fermentation condition, the modified Gompertz's equation could be used to predict the fermentation kinetics. The predicted maximum ethanol generation rate was 2.37 g L⁻¹ h⁻¹.     

The influence of carbon support porosity on the activity of PtRu/Sibunit anode catalysts for methanol oxidation

In this paper we analyse the promises of homemade carbon materials of Sibunit family prepared through pyrolysis of natural gases on carbon black surfaces as supports for the anode catalysts of direct methanol fuel cells. Specific surface area (S_BET) of the support is varied in the wide range from 6 to 415 m² g⁻¹ and the implications on the electrocatalytic activity are scrutinized. Sibunit supported PtRu (1:1) catalysts are prepared via chemical route and the preparation conditions are adjusted in such a way that the particle size is constant within ±1 nm in order to separate the influence of support on the (i) catalyst preparation and (ii) fuel cell performance. Comparison of the metal surface area measured by gas phase CO chemisorption and electrochemical CO stripping indicates close to 100% utilisation of nanoparticle surfaces for catalysts supported on low (22–72 m² g⁻¹) surface area Sibunit carbons. Mass activity and specific activity of PtRu anode catalysts change dramatically with S_BET of the support, increasing with the decrease of the latter. 10%PtRu catalyst supported on Sibunit with specific surface area of 72 m² g⁻¹ shows mass specific activity exceeding that of commercial 20%PtRu/Vulcan XC-72 by nearly a factor of 3.     

Effect of support and reduction temperature in the hydrogenation of CO2 over the Cu–Pd bimetallic catalyst with high Cu/Pd ratio

Metal-support interaction and catalyst pretreatment are important for industrial catalysis. This work investigated the effect of supports (SiO₂, CeO₂, TiO₂ and ZrO₂) for Cu–Pd catalyst with high Cu/Pd ratio (Cu/Pd = 33.5) regarding catalyst cost, and the reduction temperatures of 350 °C and 550 °C were compared. The activity based on catalyst weight follows the order of Si > Ce > Zr > Ti when reduced at 350 °C. The reduction temperature leads to the surface reconstruction over the SiO₂, CeO₂ and TiO₂ catalysts, while results in phase transition over Cu–Pd/ZrO₂. The effect of reduction temperature on catalytic performance is prominent for the SiO₂ and ZrO₂ supported catalysts but not for the CeO₂ and TiO₂ ones. Among the investigated catalysts, Zr-350 exhibits the highest methanol yield. This work reveals the importance of the supports and pretreatment conditions on the physical-chemical properties and the catalytic performance of the Cu–Pd bimetallic catalysts.     

Preparation of Ni/Pt catalysts supported on spinel (MgAl2O4) for methane reforming

MgAl₂O₄ was synthesized through hydrolysis of metallic alkoxides of Mg²⁺ and Al³⁺. The formed spinel precursor phase was calcined at temperatures between 600 and 1100 °C, for 4 h. The spinel was utilized as a Ni/Pt catalyst support. The Ni/MgAl₂O₄ catalysts (15% Ni, w/w) containing small amounts of Pt were tested for methane steam reforming. The solids were analyzed by X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂ and catalytic tests. The spinel phase was formed at temperatures above 700 °C. The addition of small amounts of Pt to Ni/MgAl₂O₄ promoted an increase in surface area. This probably caused the considerable increase in methane conversion.     

Selective hydrogen generation from real biomass through hydrothermal reaction at relatively low temperatures

The effect of additives, such as an inorganic alkali and a nickel catalyst, on the hydrothermal process was examined to generate hydrogen from biomass with high selectivity at relatively low temperatures around 400 °C. At first, a cellulose sample as model biomass was subjected to the hydrothermal process at 400 °C under 25 MPa in the presence of an alkali (Na₂CO₃) and a nickel catalyst (Ni/SiO₂). The combination of these two additives led not only to highly efficient generation of hydrogen but also to effective dissolution of CO₂ into an alkaline liquid layer. Here the molar yields of gas products from the cellulose sample were compared with the equilibrium quantities obtained using a thermodynamics calculation software. Furthermore, the hydrothermal process of real biomass, such as wood chips, organic fertilizer and food waste, in the presence of both the two additives resulted in highly selective production of hydrogen even at 400 °C.