Optimization of hydrogen production from steam reforming of biomass tar over Ni/dolomite/La2O3 catalysts

Industrially, the endothermic process of steam reforming is carried out at the lowest temperature, steam to carbon (S/C) ratio, and gas hourly space velocity (GHSV) for maximum hydrogen (H₂) production. In this study, a three-level three factorial Box-Behnken Design (BBD) of Response Surface Methodology (RSM) was applied to investigate the optimization of H₂ production from steam reforming of gasified biomass tar over Ni/dolomite/La₂O₃ (NiDLa) catalysts. Consequently, reduced quadratic regression models were developed to fit the experimental data adequately. The effects of the independent variables (temperature, S/C ratio, and GHSV) on the responses (carbon conversion to gas and H₂ yield) were examined. The results indicated that reaction temperature was the most significant factor affecting both responses. Ultimately, the optimum conditions predicted by RSM were 775 °C, S/C molar ratio of 1.02, and GHSV of 14,648 h⁻¹, resulting in 99 mol% of carbon conversion to gas and 82 mol% of H₂ yield.     

Enhanced multi-cycle CO2 capture and tar reforming via a hybrid CaO-based absorbent/catalyst: Effects of preparation,reaction conditions and application for hydrogen production

A hybrid CaO-based absorbent/catalyst (Ca–Al–Fe) for calcium looping gasification (CLG) is prepared by a two-step sol-gel method. The effects of preparation and “carbonation-calcination” conditions on cyclic carbonation performance of Ca–Al–Fe are investigated. Calcination temperature of 900 °C and calcination time of 4 h are suitable parameters for absorbent preparation. The CaO conversion of Ca–Al–Fe increases with increasing carbonation temperature below 750 °C. Under severe calcination conditions such as high temperature, high CO₂ concentration and long-term up to 40 cycles, Ca–Al–Fe still shows good cyclic CO₂ capture reactivity. Moreover, the effect of Ca–Al–Fe on tar removal enhancement is investigated in comparison with three candidate absorbents (Ca、Ca–Fe and Ca–Al). During five toluene reforming cycles, Ca–Al–Fe presents the highest average H₂ yield and the least deposited coke with an average hydrogen concentration of about 68.8%. The average toluene conversion with Ca–Al–Fe is about 26.41% higher than that using conventional CaO.     

A novel nickel catalyst supported on activated steel slags for syngas production and tar removal from biomass pyrolysis

In this paper, a nickel-based steel slag catalyst prepared by wet impregnation was used to carry out a catalytic reforming experiment with the primary volatiles produced by pyrolysis of pine sawdust. The effects of nitric acid activation, acid-base activation, Fe promoter modification, and calcination/catalytic temperature on the catalytic performance were explored. A series of catalyst characterization methods were used to analyze the catalytic activity and coke deposition resistance. The analysis results showed that the 0.5M-Ni/SS-800 catalyst had the optimal catalytic effect. The tar conversion rate reached 97.61% and the gas yield was increased by 15.3%. The production of hydrogen was even increased by 20.23%. The elements such as Ni, Fe, Ca, and Mg in the catalyst had a synergistic catalytic effect and formed active centers such as Ni–Fe alloy, Ca₂Fe₂O_5, and MgFe₂O₄, which significantly improved the catalytic activity and coke deposition resistance.     

Catalytic characteristics of innovative Ni/slag catalysts for syngas production and tar removal from biomass pyrolysis

In this study, innovative Ni-based catalysts supported by five typical slag carriers (magnesium slag (MS), steel slag (SS), blast furnace slag (BFS), pyrite cinder (PyC) and calcium silicate slag (CSS)) were prepared by wet impregnation. With the prepared catalysts and Ni/γ-Al₂O₃ catalyst, catalytic reforming of pyrolysis volatiles from pine sawdust for syngas production and tar removal was investigated. The catalysts were characterized by BET, XRD, SEM, TEM and Raman. The catalytic performances of the six catalysts were decreasing in the following order: Ni/MS > Ni/γ-Al₂O₃ > Ni/SS > Ni/BFS > Ni/CSS > Ni/PyC. Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability in terms of tar conversion (95.19%), gas yield (1.46 Nm³/kg) and CO₂ capture ability (CO₂ yield of 0.5%). Both amorphous carbon and graphite-type carbon were formed on the catalysts after catalytic reforming and the D/G ratio (the relative intensity ratio of the D-band to the G-band) was positively correlated to the catalytic activity.     

A novel process simulation model for hydrogen production via reforming of biomass gasification tar

Process modeling and simulation are very important for new designs and estimation of operating variables. This study describes a new process for the production of hydrogen from lignocellulosic biomass gasification tars. The main focus of this research is to increase hydrogen production and improve the overall energy efficiency of the process. In this study, Aspen HYSYS software was used for simulation. The integration structure presented in this research includes sections like tar reforming and ash separation (Ash), combined heat and power cycle (CHP), hydrogen sulfide removal unit (HRU), water-gas shift (WGS) reactor, and gas compression as well as hydrogen separation from a mixture of gases in pressure swing adsorption (PSA). It was found that the addition of CHP cycle and the use of the plug flow reactor (PFR) model, firstly, increased the overall energy efficiency of the process by 63% compared to 29.2% of the base process. Secondly it increased the amount of hydrogen production by 0.518 kmol (H2)/kmol Tar as compared with 0.475 of the base process. Process analysis also demonstrated that the integrated process of hydrogen production from biomass gasification tars is carbon neutral.     

A review on ethanol steam reforming for hydrogen production over Ni/Al2O3 and Ni/CeO2 based catalyst powders

Hydrogen is contemplated as an alternative clean fuel for the future. Ethanol steam reforming (ESR) is a carbon-neutral, sustainable, green hydrogen production method. Low cost Ni/Al₂O₃ and Ni/CeO₂ powder catalysts demonstrate high ESR activity. However, acidic nature of Al₂O₃ and instability of CeO₂ lead to deactivation of the catalysts easily. This article examines the research articles published on the modification of Ni by various noble and non-noble metals and on alteration of the supports by different metal oxides in detail and their effect on ESR all through 2000–2021. The ESR reaction mechanisms on Ni/Al₂O₃ and Ni/CeO₂ powder catalysts and basic thermodynamics for different possible reactions and H₂ yield are explored. Manipulation of catalyst morphology (surface area and particle size) via preparation method, selection of active metal promoter and support modifier are found to be significantly important for H₂ production and minimizing carbon deposition on catalysts.     

Study on steam reforming of coal tar over NiCo/ceramic foam catalyst for hydrogen production: Effect of Ni/Co ratio

The effect of Ni/Co ratio on the catalytic performance of NiCo/ceramic foam catalyst for hydrogen production by steam reforming of real coal tar was studied. The NiCo/ceramic foam catalyst was synthesized by deposition-precipitation (DP) method and characterized with different methods. The experiments were conducted in a two-stage fixed-bed reactor. The results showed that the reducibility of the metallic oxides in bimetallic NiCo/ceramic foam catalysts was influenced obviously by the Ni/Co ratio.Both gas and hydrogen yield increased first and then decreased with the decline of Ni/Co ratio, and the highest hydrogen yield of 31.46 mmol g^?1 was obtained when the Ni/Co ratio was 5/5. The lowest coke deposition of 0.34 wt% was generated at the same Ni/Co ratio. The lifetime test showed the catalyst maintained catalytic activity after 14 cycles (28 h), indicating the coal tar steam reforming on NiCo/ceramic foam catalyst is a promising method for hydrogen production.     

Review of catalytic supercritical water gasification for hydrogen production from biomass

Hydrogen is defined as an attractive energy carrier due to its potentially higher energy efficiency and low generation of pollutants, which can replace conventional fossil fuels in the future. The governments have invested huge funds and made great efforts on the research of hydrogen production. Among the various options, supercritical water gasification (SCWG) is a most promising method of hydrogen production from biomass. Supercritical water (SCW) has received a great deal of attention as a most suitable reaction medium for biomass gasification because it is safe, non-toxic, readily available, inexpensive and environmentally benign. However, high temperature and pressure are required to meet the minimum reaction condition. Therefore, the high operating cost has become the biggest obstacle to the development of this technology. To overcome this bottleneck, many researchers have carried out intensive research work on the catalytic supercritical water gasification (CSCWG). Based on the previous studies stated in the literature, the authors try to give an overview (but not an exhaustive review) on the recent investigations of CSCWG. Besides, the physicochemical properties of SCW and its contributions in subcritical and supercritical water reaction are also summarized.     

Steam reforming of acetic acid using Ni/Al2O3 catalyst: Influence of crystalline phase of Al2O3 support

Ni-based catalysts supported on various alumina supports with different crystalline phases (γ-, α-, θ- and δ-Al₂O₃) were prepared and the effects of crystalline phases on the catalytic performance towards acetic acid steam reforming (AASR) were investigated. An acetic acid conversion of nearly 100% was observed in all the four catalysts, and their hydrogen selectivities were in the following order: Ni/α-Al₂O₃ (90%) > Ni/γ-Al₂O₃ (79%) > Ni/δ-Al₂O₃ (53%) > Ni/θ-Al₂O₃ (25%). Using different characterization methods, the inner relationship between catalyst crystalline phase and catalytic properties was determined. Through TEM, H₂-TPR and XPS characterization, Compared with α-Al₂O₃, on the surface of other crystalline phases of Al₂O₃ support were formed NiAl₂O₄ which indicated stronger interaction intensity between these supports and Ni., and that would reduce the formation of metallic Ni. It was confirmed that metallic Ni played a core role of catalytic AASR. More metallic Ni content caused better CC bonds and CH bonds breaking capability and eventually enhanced the selectivity towards hydrogen. That would be the key reason for Ni/α-Al₂O₃ showed best hydrogen selectivity among these four catalysts.     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.     

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H₂) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H₂ production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.     

Ni/Pd-promoted Al2O3–La2O3 catalyst for hydrogen production from polyethylene terephthalate waste via steam reforming

Ni/Pd-co-promoted Al₂O₃–La₂O₃ catalysts for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR-H₂, SEM, TGA and DTA. The results showed that Ni-Pd-co-impregnated Al₂O₃–La₂O₃ catalyst has excellent activity for the production of hydrogen with a prolong stability. The feed conversion of 87% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 93.87% in the case of 10% Ni-1% Pd/Al₂O₃–La₂O₃ catalysts with an H₂ fraction of 0.60. The catalyst performance in term of H₂ selectivity and feed conversion was further investigated under various operating parameters, e.g., temperatures, feed flow rates, feed ratios and PET concentrations. It was found that the temperature has positive effects on H₂ selectivity and conversion, yet feed flow rate has the adverse effects. In addition, PET concentrations showed improved in H₂ selectivity in comparison to when only phenol as a solvent was involved. The Ni particles, which are the noble-based active species are more effective, thus offered good hydrogen production in the PET steam reforming process. Incorporation of La₂O₃ as support and Pd as a promoter to the Ni/Al₂O₃ catalyst significantly increased catalyst stability. The Ni–Pd/Al₂O₃–Al₂O₃ catalyst showed remarkable activity even after 36 h along with the production of carbon nanotubes, while H₂ selectivity and feed conversion was only slightly decreased.     

Promotional effect of Fe on perovskite LaNixFe1−xO3 catalyst for hydrogen production via steam reforming of toluene

The effect of Fe addition on catalytic activity and stability of LaNi_xFe_1−xO₃ perovskite catalyst was investigated for hydrogen production via steam reforming of tar using toluene as a model compound. The addition of Fe to LaNiO₃ catalyst at the optimum amount enhanced the catalytic performance in steam reforming of toluene. LaNi_0.8Fe_0.2O₃ catalyst shows the best performance in terms of catalytic activity and stability for 8 h of reaction time. The catalyst characterization indicates the presence of Ni-rich Ni–Fe smaller bimetallic particles, strong metal support interaction, and lower carbon deposition rate on LaNi_0.8Fe_0.2O₃ catalyst. The synergy between Ni and Fe atoms on the small Ni–Fe bimetallic particles is crucial for high activity of the LaNi_0.8Fe_0.2O₃ catalyst. In addition, the strong interaction between metal and support on the LaNi_0.8Fe_0.2O₃ catalyst can prevent metal sintering, thus, achieving high catalytic stability.     

Catalyst support effect on ammonia decomposition over Ni/MgAl2O4 towards hydrogen production

Ammonia is a prospective fuel for hydrogen storage and production, but its application is limited by the high cost of the catalysts (Ru, etc.) to decompose NH₃. Decomposing ammonia using non-precious Ni as catalysts can therefore improve its prospects to produce hydrogen. This work proposes several Ni/MgAl₂O₄ with the support properties tuned and investigates the support effect on the catalytic performance. Ni/MgAl₂O₄-LDH shows high NH₃ conversion (～88.7%) and H₂ production rate (～1782.6 mmol g^?1 h^?1) at 30,000 L. kg^?1 h^?1 and 600 °C, which is 1.68 times as large as that of Ni/MgAl₂O₄-MM. The performance remains stable over 30 h. The characterizations manifest that the high specific surface area of Ni/MgAl₂O₄-LDH can introduce highly dispersed Ni on the surface. Kinetics analysis implies promoted NH₃ decomposition reaction and alleviated H₂ poisoning for Ni/MgAl₂O₄-LDH. A roughly linear relationship is obtained by fitting the curves of dispersed Ni on the surface vs the reaction orders regarding H₂ and NH₃. This indicates that enhanced NH₃ decomposition performance can be ascribed to the strengthened NH₃ decomposition reaction and weakened H₂ poisoning by the highly dispersed Ni on the MgAl₂O₄-LDH surface. This work provides an opportunity to develop highly active and cost-effective catalysts to produce hydrogen via NH₃ decomposition.     

Solar receiver/reactor for hydrogen production with biomass gasification in supercritical water

A novel receiver/reactor driven by concentrating solar energy for hydrogen production by supercritical water gasification (SCWG) of biomass was designed, constructed and tested. Model compound (glucose) and real biomass (corncob) were successfully gasified under SCW conditions to generate hydrogen-rich fuel gas in the apparatus. It is found that the receiver/reactor temperature increased with the increment of the direct normal solar irradiation (DNI). Effects of the DNI, the flow rates and concentration of the feedstocks as well as alkali catalysts addition were investigated. The results showed that DNI and flow rates of reactants have prominent effects on the temperature of reactor wall and gasification results. Higher DNI and lower feed concentrations favor the biomass gasification for hydrogen production. The encouraging results indicate a promising approach for hydrogen production with biomass gasification in supercritical water using concentrated solar energy.     

Hydrogen production from glycerol steam reforming over Ni/La/Co/Al2O3 catalyst

Hydrogen production by steam reforming reaction of glycerol over Co/La/Ni-Al₂O₃ was studied in tubular fixed-bed reactor. The influences of operating parameters such as temperature, steam/carbon ratio, and weight hourly space velocity (WHSV) on hydrogen yield and carbon conversion were examined under atmospheric pressure. The results showed that carbon conversion increased with the increase of temperature and steam-to-carbon mole ratio (S/C). At 700°C, S/C=3:1, and WHSV=2.5h^?1, hydrogen yield and potential hydrogen yield were up to 77.64% and 89.64%, respectively; meanwhile, the carbon conversion reached 96.36%.     

Effect of La2O3 and CeO2 loadings on formation of nickel-phyllosilicate precursor during preparation of Ni/SBA-15 for hydrogen-rich gas production from ethanol steam reforming

The importance of La₂O₃ or both La₂O₃ and CeO₂ promoters on the formation of nickel phyllosilicate (Ni₃Si₄O₁₂H₂) as a precursor of Ni/SBA-15 for ethanol steam reforming (ESR) was investigated. The catalyst was made by a one-step modified conventional triblock copolymer synthesis method (pH-Adjustment with ammonium hydroxide). The prepared catalysts were characterized by N₂ adsorption/desorption isotherms, XRD, H₂-TPR, SEM-EDS and TGA-DSC techniques. The N₂ adsorption/desorption isotherms identified the mesoporous nature of the catalysts and the XRD patterns of the calcined catalysts confirmed the formation of nickel-phyllosilicate structure. The H₂-TPR analysis revealed that the La₂O₃ loading considerably increased the interaction between nickel and silica frame work of SBA-15 support. The ability of these catalysts for hydrogen production from ethanol steam reforming (ESR) was evaluated in a packed bed reactor at 650 °C. In the case of Ni/SBA-15 catalysts without and with La₂O₃ promoter, the ESR experiments experienced metal sintering and coke formation. Meanwhile, the catalytic activity of both La₂O₃ and CeO₂ promoted Ni/SBA-15 catalyst (Ni-La₂O₃-CeO₂/SBA-15) remained stable with time on stream in terms of GPR and hydrogen selectivity. The stable performance of this catalyst was explained by the strong interaction of nickel with SBA-15 promoted by La₂O₃ and the suppression of coke formation by CeO₂.     

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

In recent times, glycerol has been employed as feedstock for the production of syngas (H₂ and CO) with H₂ as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al₂O₃ catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L g_cat⁻¹ h⁻¹). Ag (3)-Ni/Al₂O₃ gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H₂ production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al₂O₃, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O₂.     

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.     

Pellet size dependent steam reforming of polyethylene terephthalate waste for hydrogen production over Ni/La promoted Al2O3 catalyst

The effect of different pellet sizes of nickel (Ni) and lanthanum (La) promoted Al₂O₃ support on the catalytic performance for selective hydrogen production from polyethylene terephthalate (PET) plastic waste via steam reforming process has been investigated. The catalysts were prepared by impregnation method and were characterized using XRD, BET, TPD-CO₂, TPR, SEM, EDX, TEM and TGA. The results showed that NiLa-co-impregnated Al₂O₃ catalyst has excellent activity for the production of hydrogen. Feed conversion of 88.53% was achieved over 10% Ni/Al₂O₃ catalyst which increased to 95.83% in the case of 10% Ni-5% La/Al₂O₃ catalysts with a H₂ selectivity of 70.44%. The catalyst performance in term of gas production and feed conversion was further investigated under various operating parameters, e.g., feed flow-rate, and catalyst pellet size. It was found that at 0.4 ml/min feed flow rate, highest feed conversion and H₂ selectivity were achieved. The Ni particles, which are the noble-based active species are highly effective, thus offered good hydrogen production in the phenol-PET steam reforming process. Incorporation of La as a promoter in Ni/Al₂O₃ catalyst has significantly increased the catalyst reusability with prolonged stability. The NiLa/Al₂O₃ catalyst with larger size showed remarkable activity due to the presence of significant temperature gradients inside the pellet compared to smaller size. Additionally, the catalyst showed only slight decrease in H₂ selectivity and feed conversion even after 24 h, although production of carbon nanotubes was evidenced on its surface.