Hydrogen production from sorption enhanced steam reforming of ethanol using bifunctional Ni and Ca-based catalysts doped with Mg and Al

This work evaluated the performance of nickel-based catalysts supported on CaO and CaO–MgO–Al₂O₃ in the sorption enhanced steam reforming of ethanol (SESRE) aiming the production of high purity H₂. The catalysts were prepared by sol-gel method and characterized by different methods: Temperature programmed reduction (TPR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with chemical element mapping, N₂ physisorption and CO₂ capture capacity determined by thermogravimetric analysis (TGA). XRD analysis showed that the predominant phases were CaO, MgO, CaCO₃, Ca(OH)₂ and NiO in the calcined samples and Ni⁰ in the reduced and passivated samples. TPR profiles indicated that all catalysts presented a high degree of reduction (Ni/CaMgAl-68 > Ni/CaMgAl-79 > Ni/Ca), although Ni/CaMgAl-X samples presented high reduction temperatures indicating the formation of NiAl₂O₄. The addition of MgO and Al₂O₃ to CaO was very beneficial since the deactivation coefficients, calculated by the TGA data modeling, decreased by a factor of 3.8 for Ni/CaMgAl-79 and by a factor of 4.3 for Ni/CaMgAl-68 when compared to the Ni/Ca catalyst. The catalytic tests in the SESRE showed that Ni/CaMgAl-79 catalyst had the best performance since it had the longest high purity hydrogen production time. In the pre-breakthrough period, the H₂ mole fractions were close to 90% for all samples during all reaction cycles. After the reaction-regeneration cycles, the average crystallite size of CaO estimated by XRD increased around 38, 6 and 35% for Ni/Ca, Ni/CaMgAl-79 and Ni/CaMgAl-68, respectively. Thus, adding a dopant to the sorbent material proved to be an effective strategy to obtain a more stable catalyst capable to produce hydrogen of high purity.     

Enhanced hydrogen production by the catalytic alkaline thermal gasification of cellulose with Ni/Fe dual-functional CaO based catalysts

A two-stage system involving alkaline thermal gasification of cellulose with Ca(OH)₂ sorbent and catalytic reforming with Ni/Fe dual-functional CaO based catalysts is proposed and applied to enhance H₂ production and in-situ CO₂ capture. The results show that the H₂ concentration is maximized at a considerably lower temperature (500 °C) than commercialized biomass gasification processes, reducing energy consumption. Sol-gel method is deemed better than impregnation method for its lower cost and higher-concentration H₂ production. Among the prepared catalysts, sol-NiCa catalyst exhibits the best performance in CO₂ absorption, resistance to carbon deposition, and cyclic stability, creating maximum H₂ concentration (79.22 vol%), H₂ yield (27.36 mmol g⁻¹ cellulose), and H₂ conversion (57.61%). Introduction of Ni rather than Fe on the CaO based catalyst promotes steam methane reforming at moderate temperature range of 400–600 °C, generating low contents of CH₄ (5.38 vol%), CO₂ (4.82 vol%), and CO (10.58 vol%).     

Sorption enhanced steam methane reforming by Ni–CaO materials supported on mayenite

Sorption enhanced steam methane reforming (SESMR), i.e. SMR with in situ CO₂-sorption, can lead to a sustainable and economical exploiting of natural gas for hydrogen production, with high purity and simultaneous sequestration of greenhouse gases. CaO-mayenite CO₂-sorbents, Ni-mayenite SMR catalysts and Ni–CaO-mayenite combined sorbent catalyst materials (CSCM) for SESMR were synthesized by wet mixing and wet impregnation methods, and characterized by means of XRD, BET/BJH, SEM/EDS, and TPR. For CSCM, an influence of CaO load on textural and Ni reducibility properties was recorded. Materials sorption capacity was measured in multicycles sorption/regeneration TGA tests: it always underwent a stabilization with cycle number increase. Reforming tests in micro-reactor scale were performed on 3 wt% to 10 wt% Ni-mayenite and selected CSCM: all Ni-mayenite always shown good performances, while for CSCM a detrimental role of CaO load on Ni catalytic activity was evidenced.     

Hydrogen rich fuel gas production by gasification of wet biomass using a CO2 sorbent

Hydrogen rich fuel gas production by gasification of wet biomass accompanied by CO₂ absorption is proposed. The paper addressed this topic, and experiments were conducted to investigate the effects of the moisture content (M), the molar ratio of Ca(OH)₂ to carbon in the biomass ([Ca]/[C]) and the reactor temperature (T) on hydrogen production and CO₂ absorption by CaO. Measurement of the calcium compounds in solid residues was carried out with XRD and SEM. The results show that directly gasifying of wet biomass not only favors hydrogen production but also promotes CO₂ absorption by CaO. For the experiment with wet biomass (M = 0.90), the H₂ yield is increased by 51.5% while the CO₂ content is decreased by 28.4% than that for experiments with dry biomass (M = 0.09). CaO plays the dual role of catalyst and sorbent. It is noteworthy that CaO reveals a stronger effect on the water gas shift reaction than on the steam reforming of methane. The increase of the reactor temperature contributes to produce more H₂, but goes against CO₂ absorption by CaO. XRD spectrum and SEM image of the solid residues further confirmed that high temperature is unfavorable to CO₂ absorption by CaO. For the new method, the optimal operating temperature is in the 923–973 K range.     

Hydrogen production via steam reforming of coke oven gas enhanced by steel slag-derived CaO

Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO₂ sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO₂ capture capacity of about 0.48 g CO₂/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe₂O₃. Product gas containing 95.8 vol% H₂ and 1.4 vol% CO, with a CH₄ conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH₄ conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH₄ conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.     

H2S effect on dry reforming of biogas for syngas production

The effect of hydrogen sulfide (H₂S) on dry reforming of biogas for syngas production was studied both experimentally and theoretically. In the experimental work, the H₂S effect on Ni‐based catalyst activity was examined for reaction temperatures ranging from 600°C to 800°C. It was found that the presence of H₂S deactivated the Ni‐based catalysts significantly because of sulfur poisoning. Although bimetallic Pt‐Ni catalyst has better performance compared with monometallic Ni catalyst, deactivation was still found. The time‐on‐stream measured data also indicated that sulfur‐poisoned catalyst can be regenerated at high reaction temperatures. In the theoretical work, a thermodynamic equilibrium model was used to analyze the H₂S removal effect in dry reforming of H₂S‐contained biogas. Calcium oxide (CaO) and calcium carbonate (CaCO₃) were used as the H₂S sorbent. The results indicated that H₂S removal depends on the initial H₂S concentration and reaction temperature for both sorbents. Although CO₂ was also removed by CaO, the results from equilibrium analysis indicated that the dry reforming reaction in the presence of CaO was feasible similar to the sorption enhanced water‐gas shift and steam‐methane reforming reactions. The simulation results also indicated that CaO was a more preferable H₂S sorbent than CaCO₃ because syngas with an H₂/CO ratio closer to 2 can be produced and requires lower heat duty.     

Improved hydrogen production performance of Ni–Al2O3/CaO–CaZrO3 composite catalyst for CO2 sorption enhanced CH4/H2O reforming

Bifunctional composite catalysts are very intrigued to produce hydrogen via CO₂ sorption enhanced CH₄/H₂O reforming. However, their hydrogen production performance declined over multiple cycles, owing to the structure collapse and the sintering of active component under high-temperature regeneration. This work reported the facile synthesis of long-lasting Ni–Al₂O₃/CaO–CaZrO₃ composite catalysts with less inert components (36 wt%) for stable hydrogen production over the multiple cycles of CO₂ sorption enhanced CH₄/H₂O reforming. The effects of reaction and regeneration temperature on the hydrogen production performance of Ni–Al₂O₃/CaO–CaZrO₃ were explored. Ni–Al₂O₃/CaO–CaZrO₃ demonstrated high activity and stability while fixing reaction temperature as 600 °C and regeneration temperature as 750 °C. Of particular importance, H₂ concentration was 98 vol% even after 10 hydrogen production cycles due to the inert component CaZrO₃ having a cross-linked structure. The distribution of CaZrO₃ in the composite as a coral-like structure inhibited the sintering of CaO through high Taman temperature and physical separation. Moreover, it provided the skeleton support and pore volume for the repeated expansion and contraction process of CaO to CaCO₃ during the cycling process. Finally, the sintering of Ni slowed down in appropriate regeneration temperature to maintain the structure of the composite catalyst, which further improved the catalyst's stability over multiple cycles.     

A novel catalyst–sorbent system for an efficient H2 production with in-situ CO2 capture

This paper presents an experimental investigation for an improved process of sorption-enhanced steam reforming of methane in an admixture fixed bed reactor. A highly active Rh/Ce_αZr_1−αO₂ catalyst and K₂CO₃-promoted hydrotalcite are utilized as novel catalyst/sorbent materials for an efficient H₂ production with in situ CO₂ capture at low temperature (450–500 °C). The process performance is demonstrated in response to temperature (400–500 °C), pressure (1.5–6.0 bar), and steam/carbon ratio (3–6). Thus, direct production of high H₂ purity and fuel conversion >99% is achieved with low level of carbon oxides impurities (<100 ppm). A maximum enhancement of 162% in CH₄ conversion is obtained at a temperature of 450 °C and a pressure of 6 bar using a steam/carbon molar ratio of 4. The high catalyst activity of Rh yields an enhanced CH₄ conversion using much lower catalyst/sorbent bed composition and much smaller reactor size than Ni-based sorption enhanced processes at low temperature. The cyclic stability of the process is demonstrated over a series of 30 sorption/desorption cycles. The sorbent exhibited a stable performance in terms of the CO₂ working sorption capacity and the corresponding CH₄ conversion obtained in the sorption enhanced process. The process showed a good thermal stability in the temperature range of 400–500 °C. The effects of the sorbent regeneration time and the purge stream humidity on the achieved CH₄ conversion are also studied. Using steam purge is beneficial for high degree of CO₂ recovery from the sorbent.     

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.     

MxOy (M = Mg,Zr, La,Ce) modified Ni/CaO dual functional materials for combined CO2 capture and hydrogenation

The integrated CO₂ capture and utilization has recently attracted attention as a promising approach to reduce CO₂ emissions as well as produce value-added chemicals and fuels. Herein, metal oxides (M_xO_y, M = Mg, Zr, La, and Ce) modified Ni/CaO dual functional materials (M-Ni/Ca DFMs) were synthesized and applied to the combined CO₂ capture and hydrogenation using a single reactor at one temperature. The La–Ni/Ca showed the highest CO₂ adsorption capacity (13.8 mmol/g), CO₂ conversion (64.3%) and CO yield (8.7 mmol/g). Results indicated that the addition of metal oxides increased the number of basic sites which played important role in efficient CO₂ capture. The high activities of M-Ni/Ca were attributed to the formation of highly dispersed small-sized Ni particles. Furthermore, the La–Ni/Ca exhibited excellent cyclic stability after 20 cycles due to the La₂O₃ as a physical barrier and a support for inhibiting the growth and sintering of CaO and Ni particles.     

Experimental investigation of improved calcium-based CO2 sorbent and Co3O4/SiO2 oxygen carrier for clean production of hydrogen in sorption-enhanced chemical looping reforming

In this study, highly pure hydrogen is produced in sorption enhanced chemical looping steam methane reforming (SE-CLSMR) using cobalt-based oxygen carrier (OC) and cerium promoted CaO-based sorbent. In addition, the CO₂ removal from a gas stream at high temperatures is investigated via calcium looping process prior to SE-CLSMR process. The prepared samples are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and energy dispersive X-ray spectroscopy (EDX) techniques. The effect of Ca/Ce molar ratio (100/0.00–0.91/0.09), sorption temperature (550–650 °C) and sorbent lifetime are studied to find the optimal sorbent. The characterization results show the uniform and orderly CeO₂ dispersed sorbent nanoparticles that notably improved the sorbent morphology compared with blank CaO. The sorption results revealed the negative effect of temperature on CO₂ uptake of all the samples. In addition, the CO₂ sorption evaluations indicate that the molar ratio of cerium to calcium plays a significant role in the stability of sorbent and improved the CO₂ sorption capacity significantly. The high CO₂ removal efficiency in the cerium modified sorbents could be due to decrease in diffusion resistance of CO₂ through the sorbent structure during the carbonation reaction. Furthermore, results show that the addition of cerium to the sorbent structure, effectively improves the thermal resistance of synthesis sorbents. The SE-CLSMR results showed that the H₂ purity could be increased up to about 95% considering Co₃O₄/SiO₂ oxygen carrier and cerium promoted calcium-based sorbent at relatively low temperature of 550 °C, which is comparable with 84% in CLR process.     

Continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production

In this study, the continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production by a simultaneous flow concept of catalyst and sorbent for reaction and regeneration using two moving-bed reactors has been evaluated experimentally. A Ni-based catalyst (NiO/NiAl₂O₄) and a lime sorbent (CaO) were used for glycerol steam reforming with and without in-situ CO₂ removal at 500 °C and 600 °C. The simultaneous regeneration of catalyst and sorbent was carried out with the mixture gas of N₂ and steam at 900 °C. The product gases were measured by a GC gas analyzer. It is obvious that the amounts of CO₂, CO and CH₄ were reduced in the sorption-enhanced steam reforming of glycerol, and the H₂ concentration is greatly increased in the pre-CO₂ breakthrough periods within 10 min both 500 °C and 600 °C. The extended time of operation for high-purity hydrogen production and CO₂ capture was obtained by the continuous sorption-enhanced steam reforming of glycerol. High-purity H₂ products of 93.9% and 96.1% were produced at 500 °C and 600 °C and very small amounts of CO₂, CH₄ and CO were formed. The decay in activity during the continuous reaction-regeneration of catalyst and sorbent was not observed.     

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO₂ capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO₂, and the solid product is CaCO₃, and the Ca(OH)₂ may be formed from the reaction of CaO with H₂O with the presence of steam in gas phase. The effect of Ca(OH)₂ and CaCO₃ on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO₃ did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)₂ may be the reason of catalytic reactivity recovery. CaCO₃ can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO₃ decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.     

Enhanced coal gasification heated by unmixed combustion integrated with an hybrid system of SOFC/GT

For clean utilization of coal, enhanced gasification by in situ CO₂ capture has the advantage that hydrogen production efficiency is increased while no energy is required for CO₂ separation. The unmixed fuel process uses a sorbent material as CO₂ carrier and consists of three coupled reactors: a coal gasifier where CO₂ is captured generating a H₂-rich gas that can be utilized in fuel cells, a sorbent regenerator where CO₂ is released by sorbent calcination and it is ready for capture and a reactor to oxidize the oxygen transfer material which produces a high temperature/pressure vitiated air. This technology has the potential to eliminate the need for the air separation unit using an oxygen transfer material. Reactors' temperatures range from 750 °C to 1550 °C and the process operates at pressure around 7.0 bar. This paper presents a global thermodynamic model of the fuel processing concept for hydrogen production and CO₂ capture combined with fuel and residual heat usage. Hydrogen is directly fed to a solid oxide fuel cell and exhaust streams are used in a gas turbine expander and in a heat recovery steam generator. This paper analyzes the influence of steam to carbon ratio in gasifier and regeneration reactor, pressure of the system, temperature for oxygen transfer material oxidation, purge percentage in calciner, average sorbent activity and oxidant utilization in fuel cell. Electrical efficiency up to 73% is reached under optimal conditions and CO₂ capture efficiencies near 96% ensure a good performance for GHG's climate change mitigation targets.     

A novel hybrid iron-calcium catalyst/absorbent for enhanced hydrogen production via catalytic tar reforming with in-situ CO2 capture

An iron-calcium hybrid catalyst/absorbent (Ca–Al–Fe) is developed by a two-step sol-gel method to enhance tar conversion, cyclic CO₂ capture and mechanical strength of absorbent for hydrogen production in calcium looping gasification. The developed catalyst/absorbent consists of CaO and brownmillerite (Ca₂Fe₂O₅) with mayenite (Ca₁₂Al₁₄O₃₃) as inert support. Comparing with three candidate absorbents without Ca₂Fe₂O₅ or Ca₁₂Al₁₄O₃₃, cyclic carbonation reactivity and mechanical strength of Ca–Al–Fe are largely promoted. Meanwhile, Ca–Al–Fe approaches the maximum conversion rate of 1-methyl naphthalene (1-MN) with enhanced hydrogen yield around 0.15 mol/(h·g) under reforming conditions of present study. Ca–Al–Fe also shows the largest CO₂ absorption and lowest coke deposition. Influences of operation variables on 1-MN reforming are evaluated and recommended conditions can be iron to CaO mass ratio of 10%, reaction temperature of 800 °C and steam to carbon in 1-MN mole ratio of 2.0. Ca–Al–Fe hybrid catalyst/absorbent presents good potential to be applied in future.     

Enhanced hydrogen-rich gas production from steam gasification of coal in a pressurized fluidized bed with CaO as a CO2 sorbent

Steam gasification of a typical Chinese bituminous coal for hydrogen production in a lab-scale pressurized bubbling fluidized bed with CaO as CO₂ sorbent was performed over a pressure range of ambient pressure to 4 bar. The compositions of the product gases were analyzed and correlated to the gasification operating variables that affecting H₂ production, such as pressure (P), mole ratio of steam to carbon ([H₂O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H₂ concentration was enhanced by raising the temperature, pressure and [H₂O]/[C] under the circumstances we observed. With the presence of CaO sorbent, CO₂ in the production gas was absorbed and converted to solid CaCO₃, thus shifting the steam reforming of hydrocarbons and water gas shift reaction beyond the equilibrium restrictions and enhancing the H₂ concentration. H₂ concentration was up to 78 vol% (dry basis) under a condition of 750 °C, 4 bar, [Ca]/[C] = 1 and [H₂O]/[C] = 2, while CO₂ (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be used as a substantially excellent CO₂ sorbent for the pressurized steam gasification of bituminous coal. For the gasification process with the presence of CaO, H₂-rich syngas was yielded at far lower temperatures and pressures in comparison to the commercialized coal gasification technologies. SEM/EDX and gas sorption analyses of solid residues sampled after the gasification showed that the pore structure of the sorbent was recovered after the steam gasification process, which was attributed to the formation of Ca(OH)₂. Additionally, a coal-CaO–H₂O system was simulated with using Aspen Plus software. Calculation results showed that higher temperatures and pressures favor the H₂ production within a certain range.     

High capacity potassium-promoted hydrotalcite for CO2 capture in H2 production

This paper presents an experimental study for a newly modified K₂CO₃-promoted hydrotalcite material as a novel high capacity sorbent for in-situ CO₂ capture. The sorbent is employed in the sorption enhanced steam reforming process for an efficient H₂ production at low temperature (400–500 ^°C). A new set of adsorption data is reported for CO₂ adsorption over K-hydrotalcite at 400 °C. The equilibrium sorption data obtained from a column apparatus can be adequately described by a Freundlich isotherm. The sorbent shows fast adsorption rates and attains a relatively high sorption capacity of 0.95 mol/kg on the fresh sorbent. CO₂ desorption experiments are conducted to examine the effect of humidity content in the gas purge and the regeneration time on CO₂ desorption rates. A large portion of CO₂ is easily recovered in the first few minutes of a desorption cycle due to a fast desorption step, which is associated with a physi/chemisorption step on the monolayer surface of the fresh sorbent. The complete recovery of CO₂ was then achieved in a slower desorption step associated with a reversible chemisorption in a multi-layer surface of the sorbent. The sorbent shows a loss of 8% of its fresh capacity due to an irreversible chemisorption, however, it preserves a stable working capacity of about 0.89 mol/kg, suggesting a reversible chemisorption process. The sorbent also presents a good cyclic thermal stability in the temperature range of 400–500 °C.     

Toluene steam reforming properties of CaO based synthetic sorbents for biomass gasification process

Biomass gasification process generates undesired Topping Atmosphere Residue (TAR), removable by catalytic steam reforming. The use of a CO₂-sorbent powder inside the reactor bed can minimize the content of carbon dioxide and carbon monoxide by enhancing the water gas shift (WGS) reaction, offering a fuel gas rich of H₂. The present study addresses the practical feasibility of such concepts, using toluene as a representative TAR and a hybrid compound Ni/CaO–Ca₁₂Al₁₄O₃₃ as reactor bed material, simultaneously acting as reforming catalyst and CO₂ sorbent. In fact, the CaO is the effective sorbent, whereas the Ca₁₂Al₁₄O₃₃ is a support for both the CaO and the active metallic Ni particles. A different synthesis route with respect to the literature has been developed for the production of the Ni/CaO–Ca₁₂Al₁₄O₃₃ and a total of three different bed reactor powders have been tested and compared: (i) a mixture of olivine and commercial nickel catalyst, (ii) a mixture of CaO–Ca₁₂Al₁₄O₃₃ and commercial nickel catalyst, and (iii) the Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent. The best performances have been observed in the latter, with toluene conversion close to 99%, and the volume fraction of hydrogen in the gas over 95%. During multi-cycle tests, the synthetic Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent exhibited superior resistance to carbon deposition and stability in toluene conversion compared to the other bed materials that suffer from decreased conversion efficiency after few cycles.     

Hydrogen production by sorption-enhanced steam reforming of acetic acid over Ni/CexZr1−xO2-CaO catalysts

The production of high purity hydrogen via the sorption-enhanced steam reforming of acetic acid, a model compound of bio-oil, was investigated in this work. A bi-functional catalyst with stable catalytic activity and CO₂-capture ability, Ni/Ce_xZr_1−xO₂-CaO, was prepared by a sol–gel method and characterized in details by BET, XRD, TPR and SEM-EDX analytic techniques. The characterization of these materials showed that the catalysts were mainly composed of Ni, Ce_xZr_1−xO₂ and CaO. As CaO loading increased, a new species, CaZrO_3, with a perovskite structure was formed. The presence of CaZrO₃ in the catalysts acted as a barrier to CaO grain growth at high temperatures and thus improved the CO₂-capture stability. These catalysts exhibited good CO₂ sorption capacity in 15 consecutive carbonation–calcination cycles, even at a high calcination temperature of 900 °C. Particularly, in case of the Ni/CZC-2.5 catalyst, 98% high purity H₂ could be obtained during the prebreakthrough stage when the catalysts were tested in the SESR of acetic acid at 550 °C with an S/C ratio of 4. In addition, high hydrogen purity was maintained over 15 cyclic reaction-calcination operations, which was mainly attributed to the uniform distribution of Ni, CaO, Ce_xZr_1−xO₂ and CaZrO₃ in the catalysts. These results indicated the great potential of the SESR technique for hydrogen production from bio-oil.     

High quality syngas production from pressurized K2CO3 catalytic coal gasification with in-situ CO2 capture

The enhanced K-catalytic coal gasification by CO₂ sorption reaction (EKcSG) was proposed to produce syngas with high content of H₂ and CH₄ and perform in-situ CO₂ capture. CO₂ is reduced dramatically with the introduction of the CaO into the reactor under typical K-catalytic coal gasification condition (3.5 MPa, 700 °C). The carbonation reaction of CaO can promote the syngas production by improving the equilibrium of the water-gas shift reaction and supplying heat for coal gasification reaction. In the presence of the CaO sorbent (Ca/C = 0.5), the CO₂ concentration in the product gas decreased from 25.61% to 12.80% compared with that without CaO. Correspondingly, the total concentration of H₂ and CH₄ is improved from 65.61% to 82.99% and the carbon conversion reached above 95%. The effect of Ca/C ratio and reaction temperature was investigated during the EKcSG process. It is considered that Ca/C ratio of 0.5 is the best proportion in terms of carbon conversion and CO₂ absorption in our experimental conditions.