Catalytic gasification of food waste in supercritical water over La promoted Ni/Al2O3 catalysts for enhancing H2 production

Ni/Al₂O₃ catalyst is the one of promising catalysts for enhancing H₂ production from supercritical water gasification (SCWG) of biomass. However, due to carbon deposition, the deactivation of Ni/Al₂O₃ catalyst is still a serious issue. In this work, the effects of lanthanum (La) as promoter on the properties and catalytic performance of Ni/Al₂O₃ in SCWG of food waste were investigated. La promoted Ni/Al₂O₃ catalysts with different La loading content (3–15 wt%) were prepared via impregnation method. The catalysts were characterized using XRD, SEM, BET techniques. The SCWG experiments were carried out in a Hastelloy batch reactor in the operating temperature range of 420–480 °C, and evaluated based on H₂ production. The stability of the catalysts was assessed by the amount of carbon deposition on catalyst surface and their catalytic activity after reuse cycles. The results showed that 9 wt% La promoter is the optimal loading as Ni/9La–Al₂O₃ catalyst performed best performance with the highest H₂ yield of 8.03 mol/kg, and H₂ mole fraction of 42.46% at 480 °C. La promoted Ni/Al₂O₃ catalysts have better anti-carbon deposition properties than bare Ni/Al₂O₃ catalyst, resulting in better gasification efficiency after reuse cycles. Ni/9La–Al₂O₃ catalyst showed high catalytic activity in SCWG of food waste and had good stability as it was still active for enhancing H₂ production when used in SCWG for the third time, which indicated that La promoted Ni/Al₂O₃ catalysts are potential additive to improve the SCWG of food waste.     

Structural effect of ZrO2 on supported Ni-based catalysts for supercritical water gasification of oil-containing wastewater

Supercritical water gasification (SCWG) is a promising technology to treat oil-containing wastewater. This study reports a Ni/ZrO₂ catalyst with mixed phase of tetragonal ZrO₂ and monoclinic ZrO₂ synthesized by a one-step sol-gel method, which shows good catalytic activity and stability in SCWG of oil mixture. The evolution of particle size, crystal structure, and pore size caused by increasing calcination temperature is demonstrated by X-ray diffraction and transmission electron microscopy. When calcined at 700 °C, Ni/ZrO₂ shows superior catalytic activity and stability in SCWG reaction, with a high carbon gasification efficiency of 91.3% at 500 °C. The characterizations of fresh and spent catalysts suggest that Ni/ZrO₂ catalyst with the fraction of monoclinic ZrO₂ around 75% would be highly active and stable in SCWG reaction. In addition, two sets of optimal gasification conditions of SCWG of oil are obtained by varying operating parameters, which provides guidance for different concentrations of oil-containing wastewater treatment.     

Supercritical water synthesized Ni/ZrO2 catalyst for hydrogen production from supercritical water gasification of glycerol

Catalysts are crucial to promote the technical feasibility of supercritical water gasification (SCWG) for H₂ production from wet biomass, yet catalysts prepared by conventional methods normally encounter sintering problems in supercritical water. Herein, a series of ZrO₂-supported Ni catalysts were tried to be prepared by supercritical water synthesis (SCWS) and evaluated for SCWG in terms of activity and property stability. The SCWS was conducted at 500 °C and 23 MPa using metal nitrates as starting materials. Effect of precursor concentration on property and catalytic performance of the SCWS-prepared catalysts for SCWG of 20 wt% glycerol were systematically studied. XRD, SEM-EDS, TEM and TGA were applied for catalyst characterization. Results verified the successful obtaining of Ni/ZrO₂ nanocatalysts with Ni crystals of 30–70 nm and ZrO₂ crystals of ~11 nm by the SCWS process, which were found to be active on the WGSR for SCWG to increase the H₂ yield as high as 155%. Importantly, the SCWS-prepared Ni/ZrO₂ catalysts exhibited excellent property stability and anti-coking ability for SCWG of glycerol.     

Effect of metal addition to Ni/activated charcoal catalyst on gasification of glucose in supercritical water

Activated charcoal supported nickel-based catalysts such as Ni/AC, Ni-Y/AC, Ni-Fe/AC, and Ni-Co/AC were formulated and their catalytic activity for the gasification of glucose in supercritical water were investigated using a packed-bed reactor at 650 °C, 28 MPa. A set of glucose gasification experiments was also carried out without catalyst and with AC to provide baseline data. Loading of small amounts of Y to the Ni/AC catalyst appeared to increase both the extent of gasification and hydrogen yield while loading of Fe or Co metal to the Ni/AC catalyst did not give any positive effect on the gasification results. Effect of catalyst composition, temperature, reactant concentration, and reactor residence time on the glucose gasification with the Ni-Y/AC catalyst was examined. Catalyst analysis indicates that adding of Y into the Ni/AC catalyst inhibited carbon formation to a great extent, thereby maintaining catalytic activity of the Ni metal for H₂ formation reactions.     

Comprehensive experimental study on supercritical water gasification of oilfield sludge: Effect of operation parameters,and catalysts on the products

Supercritical water gasification (SCWG) was adopted to treat oilfield sludge and produce syngas. The effect of temperature (400–450 °C), reaction time (30–90 min) and catalyst addition on syngas production and residual products during SCWG of oilfield sludge was studied. When increasing SCWG temperature from 400 to 450 °C with reaction time of 60 min, the H₂ yield and the selectivity of H₂ increased significantly from 0.53 mol/kg and 75.53% to 0.98 mol/kg and 78.09%, respectively. It is noteworthy that when the reaction time was too long, CO₂ and CO were converted to CH₄ with the consumption of H₂ via methanation reaction. The addition of Ni/Al₂O₃ catalyst can substantially promote the production of high-quality syngas from SCWG of oilfield sludge. The H₂ yield and its selectivity at 450 °C and 60 min were as high as 1.37 mol/kg and 84.05% with 10Ni/Al catalyst. Moreover, the catalysts with bimetal loading (Fe–Ni, Rb–Ni or Ce–Ni) were found to be beneficial for improving gasification efficiency, H₂ yield, and the degradation of organic compounds. Among them, 5 wt% Rb on 10Ni/Al catalyst performed the best catalytic activity for SCWG at 450 °C and 60 min, which had the highest H₂ yield of 1.67 mol/kg and selectivity of 86.09%. More than 90% of total organic carbon in sludge was decomposed after the SCWG with all the catalysts. These findings indicated that catalytic SCWG is a promising alternative for efficiently dealing with oilfield sludge.     

Hydrogen production by biomass gasification in supercritical water with bimetallic Ni-M/γAl2O3 catalysts (M = Cu, Co and Sn)

Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of original biomass and organic compounds for hydrogen production. In this paper, hydrogen production by SCWG of glucose over alumina-supported nickel catalysts modified with Cu, Co and Sn was studied. The bimetallic Ni-M (M = Cu, Co and Sn) catalysts were prepared by a co-impregnation method and tested in an autoclave reactor at 673 K with a feedstock concentration of 9.09 wt.%. XRD, XRF, N₂ adsorption/desorption, SEM and TGA were adopted to investigate the changes of chemical properties between Ni and Ni-M catalysts and the deactivation mechanism of catalysts. According to the experimental results, the hydrogen yield followed this order: Ni-Cu/γAl₂O₃ > Ni/γAl₂O₃ > Ni-Co/γAl₂O₃ > Ni-Sn/γAl₂O₃. The results show that Cu could improve the catalytic activity of Ni catalyst in reforming reaction of methane to produce hydrogen in SCWG. In addition, Cu can mitigate the sintering of alumina detected by SEM. Co was found to be an excellent promoter of Ni-based catalyst in relation to hydrogen selectivity.     

Screening of supported transition metal catalysts for hydrogen production from glucose via catalytic supercritical water gasification

In total 17 heterogeneous catalysts, with combinations of 4 transition metals (Ni, Ru, Cu and Co) and various promoters (e.g., Na, K, Mg, or Ru) supported on different materials (γ-Al₂O₃, ZrO₂, and activated carbon (AC)), were investigated with respect to their catalytic activity and stability for H₂ production from glucose via supercritical water gasification (SCWG). The experiments were carried out at 600 °C and 24 MPa in a bench-scale continuous-flow tubular reactor. Ni (in metallic form) and Ru (in both metallic and oxidized forms) supported on γ-Al₂O₃ exhibited very high activity and H₂ selectivity among all of the catalysts investigated for a time-on-stream of 5-10 h. With Ni20/γ-Al₂O₃ (i.e., γ-Al₂O₃ with 20 wt% Ni), a H₂ yield of 38.4 mol/kg glucose was achieved, approximately 20 times higher than that obtained during the blank test without catalyst (1.8 mol/kg glucose). In contrast, Cu and Co catalysts were much less effective for glucose SCWG reactions. As for the effects of catalyst support materials on activity, the following order of sequence was observed: γ-Al₂O₃ > ZrO₂ > AC. In addition, Mg and Ru were found to be effective promoters for the Ni/γ-Al₂O₃ catalyst, suppressing coke and tar formation.     

Hydrogen production by auto-thermal reforming of ethanol over nickel catalyst supported on metal oxide-stabilized zirconia

Metal oxide-stabilized mesoporous zirconia supports (M–ZrO₂) with different metal oxide stabilizer (M = Zr, Y, La, Ca, and Mg) were prepared by a templating sol–gel method. 20 wt% Ni catalysts supported on M–ZrO₂ (M = Zr, Y, La, Ca, and Mg) were then prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. The effect of metal oxide stabilizer (M = Zr, Y, La, Ca, and Mg) on the catalytic performance of supported nickel catalysts was investigated. Ni/M–ZrO₂ (M = Y, La, Ca, and Mg) catalysts exhibited a higher catalytic performance than Ni/Zr–ZrO₂, because surface oxygen vacancy of M–ZrO₂ (M = Y, La, Ca, and Mg) and reducibility of Ni/M–ZrO₂ (M = Y, La, Ca, and Mg) were enhanced by the addition of lower valent metal cation. Hydrogen yield over Ni/M–ZrO₂ (M = Zr, Y, La, Ca, and Mg) catalyst was monotonically increased with increasing both surface oxygen vacancy of M–ZrO₂ support and reducibility of Ni/M–ZrO₂ catalyst. Among the catalysts tested, Ni catalyst supported on yttria-stabilized mesoporous zirconia (Ni/Y–ZrO₂) showed the best catalytic performance.     

The promoting effect of La, Mg, Co and Zn on the activity and stability of Ni/SiO2 catalyst for CO2 reforming of methane

CO₂ reforming of methane into synthesis gas over Ni/SiO₂ catalysts promoted by La, Mg, Co and Zn was investigated. The catalysts were prepared by impregnation method and characterized by XRD, TPR, SEM and TG-DTA techniques. Ni-La/SiO₂ catalyst was found to exhibit high activity and excellent stability with the addition of suitable amount of La promoter, which increased the dispersion of NiO and the interaction between NiO and SiO₂. Two different types of carbon species, namely, easily oxidized carbonaceous species and inert carbon, were observed on the surface of the used catalysts. The inert carbon deposited on Ni-Mg/SiO₂ catalyst may be the main reason for its deactivation, while the principal reason for the deactivation of Ni-Co/SiO₂ catalyst might be the sintering of metallic Ni. The addition of La and Mg decreased the contribution of reverse water-gas shift reaction, leading to higher H₂ yield.     

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N₂ adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al₂O₃ catalyst yielded H₂, CO and CH₄ as main gaseous products with H₂:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O₂ as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al₂O₃ catalyst exhibited the highest carbon deposition (circa 33.0 wt%).     

Hydrogen production by biomass gasification in supercritical water over Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts. The catalytic activity and H₂ selectivity of Ni/CeO₂-γAl₂O₃ was higher than that of Ni/γ-Al₂O₃ catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO₂-γAl₂O₃ catalyst had a certain role in the inhibition of carbon deposition and coking.     

Hydrothermal gasification of microalgae over nickel catalysts for production of hydrogen-rich fuel gas: Effect of zeolite supports

A series of Ni catalysts with different zeolites were prepared by wet impregnation method and used to catalyze supercritical water gasification (SCWG) of microalgae for production of hydrogen-rich fuel gas under conditions of 430 °C, 60 min, ρ_H₂O = 0.162 g/cm³, 2 g/g Ni/zeolites. Compared with noncatalytic SCWG, the presence of Ni/zeolite could increase the hydrogen gasification efficiency and carbon gasification efficiency by promoting water–gas shift and steam reforming reactions which are mainly affected by the amount of strong acid sites and Ni, respectively. The highest carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) of 23.61% and 23.55% were achieved with Ni/HY (Na₂O, 0.8%). The gaseous produced mainly consisted of H₂ and CO₂. The H₂ content in the gaseous products varied from 27.15 to 40.51% depending on the Ni/zeolites and increased with increasing the SiO₂/Al₂O₃ molar ratio of HZSM-5, which is 2.3–3.6 times higher than that of produced without catalyst. The H₂ yield varied between 2.57 and 3.61 mmol/g depending on the Ni/zeolites and increased from 2.19 to 5.61 mmol/g with increasing the SiO₂/Al₂O₃ molar ratio from 50:1 to 170:1, which is 3.6–7.8 times higher than that of produced without catalyst. Coke formation, surface area loss, and sintering of Ni could decrease the activity of the Ni/zeolites.     

A investigation of multi-functional Ni/La-Al2O3-CeOx catalyst for bio-tar (simulated-toluene as model compound) conversion

Hydrogen production from toluene (main composition of bio-tar) steam reforming is studied using Ni-based catalysts supported on La modified Al₂O₃. Rare earths M (Ce, La, Pr, Nd) oxides are used as the modifiers to increase H₂ selectivity and reduce the formation rate of carbon deposition. These catalysts are characterized by N₂ adsorption-desorption, XRD, IR, H₂-TPR, Raman, and SEM-EDS. The characterization results reveal that M oxides (especially Ce) prevent Ni sintering, increase Ni dispersion and thus improve the catalytic activity. The addition of these modifiers also enhances the catalyst stability by inhibiting carbon deposition (improving water adsorption and OH⁻ surface mobility over La-Al₂O₃ support). It is found that the highest activity and stability are exhibited over Ni/La-Al₂O₃-CeO_x catalyst. The enhancements of the catalyst after modification can be due to the improved textural properties, the stronger metal-support interaction and excellent anti-carbon ability. Ni/La-Al₂O₃-CeO_x catalyst can be considered as a multi-function catalyst.     

Preparation of nanocrystalline Zr,La and Mg-promoted 10% Ni/Ce0.95Mn0.05O2 catalysts for syngas production via dry reforming reaction

The influence of the various promoters (Zr, La and Mg) on the physicochemical and catalytic characteristics of the 10% Ni/Ce_0.95Mn_0.05O₂ solid solution catalyst were investigated in methane dry reforming at atmospheric pressure. The co-precipitation method was employed for the synthesis of the catalyst carrier. The catalysts were characterized by BET, XRD, H₂-TPR and TPO analyses. The obtained results revealed that the addition of the promoters increased the BET surface area and the highest BET surface area was related to the catalyst promoted by La (58.99 m²/gr). The results of the TPR analysis showed that the broad peak related to the reduction of NiO species was shifted to the higher temperature, indicating the enhancement of the interaction between NiO particles and the support due to the addition of the promoter. The obtained results indicated that the addition of Mg improved the activity (CH₄ conversion (%) = 67 at 700 °C) and stability and reduced the amount of deposited carbon. Furthermore smaller Ni crystalline size was related to the catalyst promoted by Mg (10.0 nm). The highest and the lowest amount of carbon deposition was observed on the 10Ni/Ce_0.95Mn₀.₀₅O₂ and 10Ni/Ce_0.85Zr_0.10Mn_0.05O₂ catalysts, respectively.     

The effect of La2O3 and CeO2 modifiers on properties of Ni–Al catalysts for LNG prereforming

Ni/La–Al₂O₃ and Ni/Ce–Al₂O₃ catalysts with a small amount of promoters intended for prereforming of LNG were characterized by XRF, N₂ adsorption-desorption, XRD, H₂ chemisorption, HRTEM and XPS. The catalytic activity was evaluated in methane steam reforming both in the kinetic and diffusion regime, at temperatures characteristic of pre-reforming. Carbonaceous deposit was analysed by TPO-MS method. The nature and location of the coke were studied by HRTEM.La or Ce addition into Ni–Al system causes the increase of the active surface area of Ni by enhancing its dispersion. Studies at kinetic regime have shown that the promoted catalysts have almost twice the activity than reference Ni–Al catalyst. This effect was not confirmed by measurements in the diffusion regime on whole catalyst tablets. Almost identical textural properties of catalysts and diffusive limitations related to them but not the catalytic properties of the material itself appeared to be crucial factors. The presence of La (but not Ce) causes a significant increase in resistance to coking.     

Bioethanol/glycerol mixture steam reforming over Pt and PtNi supported on lanthana or ceria doped alumina catalysts

The catalytic activity of Pt and PtNi catalysts supported on γ-Al₂O₃ modified by La and Ce oxides was investigated in the steam reforming of ethanol/glycerol mixtures. In general, all the catalysts fully converted the glycerol at the temperatures tested. However, the conversion of ethanol depended on the reaction temperature and catalyst type. The conversion into gaseous products operating at 500 °C and 450 °C was 100% using the most active catalysts (PtNiAl6La and PtNiAl10Ce). These two bimetallic catalysts gave H₂ yields close to those predicted by thermodynamic equilibrium at these temperatures. However, when the reaction temperature was lowered to 400 °C, these catalytic systems and the PtNiAl one recorded a significant decrease in ethanol conversion and H₂ yield, which moved away from the thermodynamic equilibrium value. This deviation was due to intermediate liquid products (acetaldehyde, acrolein, etc.) not being further reformed and the formation of other gaseous ones (light alkanes and ethylene). PtNiAl10Ce catalyst presented the highest conversion into gas at 400 °C, resulting in the largest H₂ yield, followed by PtNiAl6La and PtNiAl catalysts. This order is in agreement with the Ni/Al surface atomic ratio measured by XPS technique in reduced samples. However, filamentous carbon nanotubes were detected but this carbon type maintained the active sites accessible for reactants, since TEM and TGA results showed that the density of this carbon was lower for PtNiAl₁₀Ce catalyst. Pt catalysts presented lower activity than PtNi catalysts possibly due to the formation of carbon nanotubes, which covered some metallic active sites.     

Insight into the anti-coking ability of NiM/SiO2 (M=ZrO2, Ru) catalyst for dry reforming of CH4 to syngas

The development of Ni-based catalysts with outstanding anti-coking ability is necessary for realizing the industrial application of dry reforming of CH₄ (DRM) to syngas. Here, a facile combustion method with unique characteristic was employed to prepare the Ni/SiO₂ catalyst with different promoters (ZrO₂ or Ru). The effects of Ni particle size and promoter (ZrO₂ or Ru) on the anti-coking ability of Ni/SiO₂ catalyst were examined. The XRD and TEM results showed that improved Ni dispersion can be obtained via the facile combustion method, accompanying with enhanced metal-support interaction and CO₂ adsorption capacity confirmed by H₂-TPR and CO₂-TPD, respectively. In comparison with Ni-IMP catalyst (prepared via the traditional impregnation method), the carbon deposition over Ni–C catalyst (prepared via the combustion method) decreased by 67% (from 2.7 to 0.9 mg _{carbon deposition}·g^?1_CH4) as a result of the small Ni particles. The H₂-TPR and XPS results revealed the interaction between promoter (ZrO₂ and Ru) and Ni. The addition of ZrO₂ can enhanced the CO₂ activation ability of catalyst and the formed oxygen species can facilitate the elimination of carbon species, further decreasing the carbon deposition compared with Ni–C catalyst. The best catalytic performance with least carbon deposition (only 0.4 mg _{carbon deposition}·g^?1 _CH4) is achieved on the NiRu–C catalyst. The slower CH₄ dissociation rate and the improved CO₂ activation benefited from Ru can bring in the better balance between the carbon formation and elimination, leading to the best anti-coking ability of catalyst.     

Effect of CaO–ZrO2 addition to Ni supported on γ-Al2O3 by sequential impregnation in steam methane reforming

Ni catalysts supported on (CaO–ZrO₂)-modified γ-Al₂O₃ were prepared by sequential impregnation. The effects of varied CaO to ZrO₂ mole ratios at 0, 0.20, 0.35, 0.45, and 0.55 on the activity and stability of the modified Ni catalysts were studied. As a result of using CaO–ZrO₂ as a promoter, each catalyst contained CaO–ZrO₂ at only 5%. γ-Al₂O₃ used as support was modified by CaO–ZrO₂ before the deposition of nickel oxide. The addition of CaO–ZrO₂ at an optimum ratio was expected to improve the stability of Ni catalysts due to the decrease of carbon formation resulting from carbon gasification. All the fresh catalysts were characterized by ICP, XRD, BET surface area, TGA in H₂, and TPR before catalytic testing in steam methane reforming at 600 °C. The spent catalysts were examined by TEM and TGA to observe the catalysts deactivation. The identification of CaO–ZrO₂ phases indicated that CaO and ZrO₂ reacted with each other to be monoclinic solid solution ZrO₂, CaZr₄O₉, CaZrO₃, and CaO corresponding to the phase diagram of CaO–ZrO₂. The existence of CaZrO₃ for 0.55 mol ratio of CaO/ZrO₂ enhanced activity in steam methane reforming because oxygen vacancies in CaZrO₃ greatly preferred the water adsorption creating the favorable conditions for carbon gasification and, then, water gas shift. The prominence and continued existence of these two reactions on the Ni catalysts leads to the particular increase of H₂ yield. Moreover, the increasing amount of CaZrO₃ in the Ni catalysts significantly improved carbon gasification. However, the Ni catalysts with CaZrO₃ showed whisker carbon after catalytic testing; this carbon specie has not been tolerated in steam methane reforming. Therefore, these results significantly differed from the hypothesis.     

Hydrogen production from catalytic steam reforming of bio-oil aqueous fraction over Ni/CeO2–ZrO2 catalysts

A series of composite catalysts Ni/CeO₂–ZrO₂ were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance during hydrogen production by steam reforming bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogen production performance of Ni/CeO₂–ZrO₂ catalysts were examined. The obtained results were compared with commercial nickel-based catalysts (Z417). The best performance of Ni/CeO₂–ZrO₂ catalyst was observed when the Ni and Ce loaded weight were 12% and 7.5% respectively. At W/B = 4.9, T = 800 °C, H₂ yield reaches the highest of 69.7% and H₂ content of 61.8% were obtained. Under the same condition, H₂ yield and H₂ content were higher than commercial nickel-based catalysts (Z417).     

Stability and activity of a co-precipitated Mg promoted Ni/Al2O3 catalyst for supercritical water gasification of biomass

We have investigated the stability and activity of a co-precipitated Mg promoted Ni/Al₂O₃ catalyst (Ni-Mg-Al) for supercritical water gasification (SCWG) of various biomass model compounds and real biomass. Phase stability and activity recovery of the Ni-Mg-Al catalyst were first compared with a catalyst prepared by impregnation method. It was found that the co-participated catalyst showed higher activity recoveries than the impregnated catalyst due to the stable Ni crystal size. Then, effects of SCWG variables including heating up rate, gasification temperature, catalyst loading amount and feedstock concentration, on the non-catalytic and catalytic gas yields and gasification efficiencies of glucose and phenol were evaluated. Results demonstrated that the presence of sufficient amount of Ni catalyst could realize complete carbon gasification of different organics, including phenol and real biomass. Catalyzed by Ni, CH₄ was the more favored produced gas at 400–500 °C while H₂ yields were more abundant at 500–600 °C. Without catalyst, carbon gasification efficiencies of SCWG of different feedstock were in the order: glycerol > glucose > cellulose ≈ corncob ≈ poplar leaf ≈ sawdust > phenol, while those catalyzed by Ni were in the order: glycerol ≈ glucose ≈ cellulose ≈ phenol > corncob ≈ poplar leaf ≈ sawdust, illustrating that the co-precipitated NiMgAl catalyst is more active on catalyzing the gasification of water-soluble organics than real biomass.