Sorption Enhanced Steam Reforming Research Articles

Hydrogen Production from the Carbon Dioxide Sorption-Enhanced Steam Reforming of Biogas Over a Ni-Based Hybrid Material with a Calcium Oxide Sorbent

Hydrogen Production from the Carbon Dioxide Sorption-Enhanced Steam Reforming of Biogas Over a Ni-Based Hybrid Material with a Calcium Oxide Sorbent

Ni-CaO-CaZrO3 bi-functional materials for high purity hydrogen production via sorption enhanced steam reforming of ethanol

Ethanol is an ideal hydrogen carrier, which can be converted to hydrogen-rich syn-gas via the steam reforming reaction. Sorption-enhanced steam reforming is a promising approach to produce high-purity hydrogen by mixing the sorbent and catalyst particles. The idea of bi-functional materials, loading both sorption and catalytic site in a single particle, could transform the inter-particle heat-mass transfer to intra-particle heat-mass transfer. This work studied the sorption-enhanced steam reforming of ethanol (SESRE) over Ni-CaO-CaZrO3 bi-functional catalysts containing sorption and catalytic sites. Bi-functional Ni-CaO-CaZrO3 catalysts were synthesized using a simple sol-gel technique. The influence of operating conditions including temperature, steam-to-carbon ratio (S/C) and weight hourly space velocity (WHSV) on Ni10-Ca90Zr10 bi-functional materials were discussed. The operating condition with a temperature of 600 °C, weight hourly space velocity of 0.34 h−1 and steam-to-carbon ratio of 3 was the most suitable reaction condition for hydrogen production in this study. Over the optimized operation conditions, the influence of Ni loadings on hydrogen production performance was further studied. The result indicated that 10 wt% is the best Ni loading in this study for Ni-CaO-CaZrO3, which enables >95% hydrogen purity in the gaseous product in the pre-breakthrough stage, with the longest breakthrough time (90 min). Furthermore, under the best operation conditions, the Ni10-Ca90Zr10 displayed excellent stability over 10 cyclic tests. In the 10th cycle, about 90% hydrogen purity was constantly obtained for at least 60 min during the pre-breakthrough stages. This study demonstrated that the Ni10-Ca90Zr10 bi-functional material is effective and stable for producing hydrogen from ethanol and has the potential to establish a method of generating clean energy with minimal carbon emission.

Green hydrogen production from biomass – A thermodynamic assessment of the potential of conventional and advanced bio-oil steam reforming processes

Steam reforming of bio-oil derived from biomass pyrolysis is one of the most promising methods for the production of green hydrogen with minimal carbon footprint. In this context, this work investigates the thermodynamic potential of hydrogen production from bio-oil steam reforming. Four routes – conventional steam reforming (CSR) and three advanced reforming processes – sorption-enhanced steam reforming (SESR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR) - were modeled for this purpose. Bio-oil was modeled as a complex mixture of model compounds belonging to all major oxygenate families in order to have a closer resemblance with raw bio-oil. CaO was selected as the sorbent, while NiO was selected as oxygen carrier. Furthermore, the effect of process parameters such as steam to carbon, sorbent to carbon, oxygen carrier to carbon ratios, and reforming temperature was explored. H2 purity and yield along with energy demand, served as the parameters for comparing the performance of the four processes. SESR provided the highest H2 yield (0.216 kgH2 kgBio-oil−1) among all the processes under optimum conditions along with a purity greater than 99 %. CLSR, meanwhile, had the lowest H2 yield and purity (0.178 kgH2 kgBio-oil−1 and 64.6 %, respectively). The combined SE-CLSR process had H2 yield greater than both CSR and CLSR (0.197 kgH2 kgBio-oil−1) and a H2 purity greater than 99 %. High in-situ heat generation was noted in the reforming reactor for both SESR and SE-CLSR, pointing towards a good potential for auto-thermal operation. Overall, SE-CLSR process is a highly intensified process with substantially lower energy requirements than all the other processes. The results highlight that by combining CO2-sorption and chemical looping with traditional reforming, H2 can be obtained in higher yields and purity and lower energy consumption.

Sorption-enhanced steam reforming of propane using bifunctional Ni/CaO, Ni/CaO-CaZrO3, and Ni/CaO-Ca2SiO4 catalysts

In this study, the performance of bifunctional catalysts of Ni over CaO, CaO-CaZrO3 and CaO-Ca2SiO4 was evaluated in CO2 capture and sorption-enhanced steam propane reforming cycles. Ni/CaO, Ni/CaO-CaZrO3, and Ni/CaO-Ca2SiO4 catalysts/sorbent were synthesized by sol-gel process. X-ray diffraction (XRD) results showed the formation of CaZrO3 and Ca2SiO4 in the catalysts. The thermal stability performance of the samples was evaluated in CO2 capture and sorption-enhanced steam propane reforming cycles. Both tests confirmed a significant improvement of the performance during both CO2 capture and steam propane reforming with the addition of Zr and Si. This effect can be attributed to the minimization of CaO sintering due to the higher thermal stability added by the formation of CaZrO3 and Ca2SiO4. In addition, Ni/CaO-CaZrO3 sample presented the highest stability during sorption-enhanced steam propane reforming cycles, with pre-breakthrough time close to 50 min and H2 yields over 90 vol.% in the pre-breakthrough period and close to 71% in the post-breakthrough, in all reaction cycles. Therefore, the results showed that the formation of the mixed oxides CaZrO3 and Ca2SiO4 improved the thermal stability of the catalysts, which can be good materials for sorption-enhanced steam propane reforming process.

Effect of H2S on biogas sorption enhanced steam reforming using a Pd/Ni-Co catalyst and dolomite as a sorbent

To achieve net zero carbon emissions from energy systems, biogas has become an attractive renewable resource for hydrogen production. The sorption enhanced steam reforming (SESR) process is proposed to produce high-purity hydrogen from biogas, enabled by combining the catalytic reforming reaction with the simultaneous CO2 removal by sorption in a single reactor. One of the most critical challenges in using biogas in conventional reforming processes is the presence of H2S since it may deactivate the reforming catalyst. Here we experimentally study the effect of the biogas H2S concentration on the H2 production by SESR, i.e., accounting for the presence of a CaO-based solid sorbent. This work was performed in a fixed-bed reactor using a Pd/Ni-Co hydrotalcite-like material (HT) catalyst and dolomite as CO2 sorbent. Biogas (60CH4/40CO2 vol.%) with different concentrations of H2S (150, 350, 500 and 1000 ppm) was evaluated. The catalyst did not deactivate for biogas H2S concentrations of 150 and 350 ppm during five cycles of the SESR process. However, a slight decrease in the catalyst activity was detected under higher sulfur concentrations after the third SESR cycle. Sulfur was detected in the spent catalyst and sorbent materials, with a higher proportion in the sorbent for the highest H2S concentration tested (1000 ppm). H2 yield decreased by 10.8% and 4.5% points for biogas H2S concentrations of 500 and 1000 ppm after five cycles, respectively, while H2 purity decreased by only 3 vol.% and 2 vol.% points, respectively.

A Comparative Study of Eggshell and Commercial Sorbent-Based Catalysts through Synthesis and Characterization for SESR Process

Hydrogen is a clean and valuable energy carrier, and there is growing consensus that a hydrogen-based economy could be the key to ensuring the long-term reliability and environmental friendliness of the world’s energy supply. There are a variety of methods and technologies that may be used to produce hydrogen; among them, sorption-enhanced steam reforming is regarded as the way that is the most effective. For the purpose of making a decision about which catalysts to employ in SESR in the future, this study compared three distinct kinds of catalysts. The wet impregnation method was used to manufacture the waste-derived CaO-implemented Ni-based catalysts, which were then used in sorption-enhanced steam reforming (SESR) to produce hydrogen (H2). X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetric analyses (TGA) were used to analyze the catalysts. XRD results showed that the crystallinity behavior for all types of catalysts such as 10NMA, 10NCMA-E, and 10NCMA was identical. The spinel compounds such as NiAl2O4 and MgAl2O4 were identified in all three types of catalysts. At high temperatures, such as at 800 °C, all catalysts were stable, evident from TGA results. During three sorption cycles, the 10NCMA-based catalyst demonstrated the highest sorption capacity among the three varieties of catalysts, followed by the 10NCMA-E catalyst. During the first, second, and third calcination cycles, the 10NCMA-based catalyst released 23.88%, 22.05%, and 23.33% CO2, respectively. 10NCMA-E can be a potential catalyst for the SESR process by decreasing the material manufacturing cost and overall cost of the SESR process.

Recent advances and prospects in high purity H2 production from sorption enhanced reforming of bio-ethanol and bio-glycerol as carbon negative processes: A review

Hydrogen has wide applications in the chemical and petroleum industries and is a clean energy carrier for electrical power generation and transportation. However, in current industries, H2 is mainly obtained from the steam reforming of natural gas and coal gasification, which resulted in huge emissions of CO2 (greenhouse gasses) and high energy consumption for H2 purification. Hence, developing H2 production technology in sustainable routes with low carbon emissions is still urgent. Sorption-enhanced steam reforming of bio-ethanol (SESRE) and sorption-enhanced steam reforming of bio-glycerol (SESRG), which coupled in-situ CO2 capture with the steam reforming of bio-ethanol or bio-glycerol, are promising strategies to yield high purity of H2 without emitting CO2 into the atmosphere. In these strategies, high purity of H2 can be produced when the high energy-consumption process such as H2 purification is avoided; besides, negative CO2 emissions can be achieved when the captured CO2 is used or sequestered. The catalysts play a pivotal role in the steam reforming processes, and the dual-functional materials (DFMs) are well regarded as the most promising solid catalysts that contribute to high-purity H2 production and CO2 capture. Thus far, there is no criterion to guide DFMs engineering for H2 generation in the SESRE and SESRG processes. Hence, in this work, a comprehensive review of the recent advances and prospects in SESRE and SESRG is presented, which provides constructive insight into the development of SESRE and SESRG technology. The optimum operating conditions in the SESRE and SESRG systems are analyzed via thermodynamics and kinetics, and the recent research progress of the DFMs is critically reviewed. Furthermore, the reforming reaction pathways and reaction mechanisms were discussed to improve the understanding of DFMs design. Finally, the prospect and challenges in the SESRE and SESRG strategies are outlooked.

Sorption-enhanced steam reforming of toluene using multifunctional perovskite phase transition sorbents in a chemical looping scheme

Sorption-enhanced steam reforming (SESR) of toluene (SESRT) using catalytic CO2 sorbents is a promising route to convert the aromatic tar byproducts formed in lignocellulosic biomass gasification into hydrogen (H2) or H2-rich syngas. Commonly used sorbents such as CaO are effective in capturing CO2 initially but are prone to lose their sorption capacity over repeated cycles due to sintering at high temperatures. Herein, we present a demonstration of SESRT using A- and B-site doped Sr1−x A’ x Fe1−y B’ y O3−δ (A’ = Ba, Ca; B’ = Co) perovskites in a chemical looping scheme. We found that surface impregnation of 5–10 mol% Ni on the perovskite was effective in improving toluene conversion. However, upon cycling, the impregnated Ni tends to migrate into the bulk and lose activity. This prompted the adoption of a dual bed configuration using a pre-bed of NiO/γ–Al2O3 catalyst upstream of the sorbent. A comparison is made between isothermal operation and a more traditional temperature-swing mode, where for the latter, an average sorption capacity of ∼38% was witnessed over five SESR cycles with H2-rich product syngas evidenced by a ratio of H2: CO x > 4.0. XRD analysis of fresh and cycled samples of Sr0.25Ba0.75Fe0.375Co0.625O3-δ reveal that this material is an effective phase transition sorbent—capable of cyclically capturing and releasing CO2 without irreversible phase changes occurring.

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.

Sorption enhanced steam reforming (SESR) of raw bio-oil with Ni based catalysts: Effect of sorbent type, catalyst support and sorbent/catalyst mass ratio

This work analyzes the effect of sorbent type (dolomite or CaO/mayenite), catalyst type (Ni/Al2O3 obtained upon reduction of a NiAl2O4 spinel or Ni/CeO2 prepared by wet-impregnation) and sorbent/catalyst ratio (4, 10 and 20) in the sorption enhanced steam reforming (SESR) of a real raw bio-oil. The experiments were performed in a continuous reaction system with two units: a thermal treatment unit at 500 °C for real bio-oil volatilization and controlled deposition of pyrolytic lignin, and a fixed-bed reactor for the SESR on line of the remaining oxygenates at 600 °C with steam-to‑carbon (S/C) ratio of 2.6. Furthermore, the causes of the unavoidable catalyst deactivation have been determined by several techniques. The sorbent activity for oxygenates decomposition/cracking reactions competes with the catalyst activity for reforming reactions and affects the morphology and location of the coke, thus affecting the catalyst stability. The combination of dolomite (less active for oxygenates decomposition than CaO/mayenite) and Ni/Al2O3 catalyst (with higher activity for real bio-oil reforming than Ni/CeO2) is the better choice. With space time of 0.15 gcatalyst·h/goxygenates, a dolomite/NiAl2O4 mass ratio of 10 allows producing a gas stream with almost 100% H2 for 30 min with high stability.

Process Simulations of High-Purity and Renewable Clean H2 Production by Sorption Enhanced Steam Reforming of Biogas

Renewable clean H2 has a very promising potential for the decarbonization of energy systems. Sorption enhanced steam reforming (SESR) is a novel process that combines the steam reforming reaction and the simultaneous CO2 removal by a solid sorbent, such as CaO, which significantly enhances hydrogen generation, enabling high-purity H2 production. The CO2 sorption reaction (carbonation) is exothermic, but the sorbent regeneration by calcination is highly endothermic, which requires extra energy. Biogas is one of the available carbon-neutral renewable H2 production sources. It can be especially relevant for the energy integration of the SESR process since, due to the exothermic sorption reaction, the CO2 contained in the biogas provides extra heat to the system, which can help to balance the energy requirements of the process. This work studies different process configurations for the energy integration of the SESR process of biogas for high-purity renewable H2 production: (1) SESR with sorbent regeneration using a portion of the produced H2 (SESR+REG_H2), (2) SESR with sorbent regeneration using biogas (SESR+REG_BG), and (3) SESR with sorbent regeneration using biogas and adding a pressure swing adsorption (PSA) unit for hydrogen purification (SESR+REG_BG+PSA). When using biogas as fuel (Cases 2 and 3), these configurations were studied using air and oxy-fuel combustion atmospheres in the sorbent regeneration step, resulting in five case studies. A thermodynamic approach for process modeling can provide the optimal process operating conditions and configurations that maximize the energy efficiency of the process, which are the basis for subsequent optimization of the process at the practical level needed to scale up this technology. For this purpose, process simulations were performed using a steady-state plant model developed in Aspen Plus, incorporating a complex heat exchanger network (HEN) to optimize heat integration. A comprehensive parametric study assessed the effects of biogas composition, temperature, pressure, and steam to methane (S/CH4) ratio on the process performance represented by the selected key performance indicators, i.e., H2 purity, H2 yield, CH4 conversion, cold gas efficiency (CGE), net efficiency (NE), fuel consumption for the sorbent regeneration step, and CO2 capture efficiency. H2 with a purity of 98.5 vol % and a CGE of 75.7% with zero carbon emissions can be achieved. When adding a PSA unit, nearly 100% H2 purity and CO2 capture efficiency were achieved with a CGE of 77.3%. The use of oxy-fuel combustion during regeneration lowered the net efficiency of the process by 2.3% points (since it requires an air separation unit) but allowed the process to achieve negative carbon emissions.

Modelling of sorption-enhanced steam reforming (SE-SR) process in fluidised bed reactors for low-carbon hydrogen production: A review

Sorption-enhanced steam reforming (SE-SR) offers lower capital costs than conventional steam reforming with carbon capture, which arises from the compact makeup that allows reforming and CO2 capture to occur in a single reactor. However, the technology readiness level (TRL) of SE-SR technology is currently low and large-scale deployment can be expedited by ramping up activities in reactor modelling and validation at pilot scale. This work first explores the concept of SE-SR technology, then the experimental activities and pilot tests performed for this technology, followed by the review of progress made on SE-SR modelling. It was found that the Eulerian-Eulerian two-fluid model is the most popular approach widely adopted for modelling SE-SR in fluidised bed reactors. However, the averaging method used to close equations ignores flow details at particle level and simplifies the particle system. Moreover, while hydrogen purity and yield have been predicted within an acceptable error, larger errors for CO2 gas output relative to experimental data have been reported for this model type. Limitations and future perspectives for reactor designs and the various models and modelling approaches are also analysed, to provide guidance and advance research, modelling and scaleup of SE-SR technology.

Rice Husk Ash-Derived Ca-Mg-Modified Silicate as Support for Ni-Co for Hydrogen Production by Sorption-Enhanced Steam Reforming of Bioethanol

A multipurpose catalyst made of nickel and cobalt supported on silicate-based material modified by Ca and Mg was developed and used in sorption-enhanced steam reforming of (bio)-ethanol (SESRE). In SESRE, steam reforming and CO2 conversion to carbonates occur together to yield clean hydrogen. The catalyst was designed using silica sourced from rice hull ash (RHA) by oxidation and, subsequently, Ni and Co were loaded by the wet-impregnation technique. Three catalysts, namely, Ni/Ca-Mg silicate, Co/Ca-Mg silicate, and Ni-Co/Ca-Mg silicate, were synthesized with different metal loadings (5–15% w/w), among which 10 %Ni-10% Co/Ca-Mg silicate was the most active and selective. Various characterization techniques were used to determine the physico-chemical properties of 10% NI-10% Co/Ca-Mg silicate. CO2-sorption capacity and adsorption breakthrough time were measured. An adsorption capacity of 7.4 mol CO2/kg sorbent and a breakthrough time of 58 min at T = 723 K were observed with hydrogen production at 88 mol %. The catalyst was evaluated and optimized using such parameters as temperature, S/C ratio, and space velocity. The catalyst was tested for its robustness and found to be stable for 10 cycles. 10% Ni-10% Co/Ca-Mg yielded the best hydrogen output under the optimized operating conditions.

Comparison of the NiAl2O4 derived catalyst deactivation in the steam reforming and sorption enhanced steam reforming of raw bio-oil in packed and fluidized-bed reactors

The choice of appropriate reactors and reforming strategies is key to make progresses on scaling up H2 production processes from raw bio-oil. This work compares the performance (conversion, product yields and deactivation) of packed-bed and fluidized-bed reactors (PBR and FBR, respectively) using a NiAl2O4 spinel derived catalyst for the H2 production from raw bio-oil via steam reforming (SR) and sorption enhanced SR (SESR, with dolomite to capture CO2). The experiments were carried out at 600 °C; steam/carbon ratio, 3.4; space time, 0.15 h; time on stream, 5 h; dolomite/catalyst ratio, 10 (SESR runs); and with prior thermal separation of the pyrolytic lignin from the raw bio-oil. The initial H2 yields are 80 % and 69 % in the SR runs with PBR and FBR, respectively, and 99 % and 92 % in the CO2 capture period (of 30 min duration) of the SESR runs in the PBR and FBR, respectively. The lower H2 yield in the FBR is due to the less efficient gas–solid contact (bubbling or slugging phenomena). Based on the analysis of the spent catalysts with varied techniques the catalyst deactivation is related to the coke deposition, whose quantity and nature (amorphous or structured) depends on the reactor type and reforming strategy. The catalyst deactivation is slower in the FBR due to the rejuvenation of the catalyst surface by the moving particles that favor external coke gasification. The presence of dolomite prolongs the period of stable catalyst activity in both reactors with different effects on the coke quantity and nature. The results are of interest to advance on scaling up the SESR process that would require a FBR integrated with a regeneration unit for the catalyst and sorbent.

Simulation analysis of bio-oil reforming for co-production syngas and high purity H2 or CO2 with chemical looping processes

Chemical looping allows for the production of different products, such as syngas, high-purity hydrogen and high concentration CO2, through a single process without the need for separation. In this study, a detailed analysis is investigated by utilizing Aspen Plus software to explore the feasibility of bio-oils efficient utilization in four chemical looping processes. The Sorption Enhanced Steam Reforming (SESR) process for syngas production with CO2 capture can be modified into an autothermal process by combusting a fraction of the syngas, leading to a syngas yield of 11.04 (mol/mol fuel) and a CO2 capture capacity of 4.18 (mol/mol fuel). The Calcium and Chemical Looping Reforming (CaL-CLR) process is a unique approach to attaining the greatest syngas yield of 11.31 (mol/mol fuel) and capturing the highest CO2 of 5.40 (mol/mol fuel) simply by adjusting the flow rate of NiO oxygen carrier to realize autothermic reforming without compromising the syngas output. Nevertheless, the integration of NiO and air reactor (AR) will lead to increased financial and operational outlays. For co-production of syngas and high-purity hydrogen, the Three-Reactors Chemical Looping Hydrogen (TR-CLH) process can produce high-purity hydrogen with 5.70 (mol/mol fuel) under autothermal conditions, but the syngas yield and purity are low. The Chemical Looping Reforming and Water Splitting (CLRWS) process has the potential to create a substantial syngas yield, up to 9.63 (mol/mol fuel), as well as a considerable flow rate of high-purity hydrogen, 8.42 (mol/mol fuel). It is clear that this process is more successful than other processes available; however, the excessively high temperature of the fuel reactor (FR) impedes its further utilization.

Sorption enhanced steam reforming of ethanol for hydrogen production, over Mg/Al hydrotalcites modified with K

Sorption-enhanced ethanol steam reforming is an interesting alternative, to produce high purity H2. In this study, potassium promoted hydrotalcites are compared for sorption-enhanced ethanol steam reforming reaction under cyclic operation, performing sorbent regeneration at reaction temperature which is a great advantage to reduce process energy requirements. It is found that potassium promoted hydrotalcites have higher CO2 sorption capacity compared to unpromoted ones, due to the higher concentration of intermediate and strong basic sites. The hydrotalcite modified with 15 wt% potassium shows the best performance on multicyclic CO2 sorption-desorption (sorption capacity = 0.167 molCO2/kgsorbent). Therefore, there is an optimum loading of potassium, for which the opposite effects of reduction in surface area and enhanced basicity are balanced. Finally, potassium promoted hydrotalcites are tested under cyclical ethanol reforming process with simultaneous adsorption of CO2 followed by regeneration in N2 at reaction temperature (500 °C). At short reaction times (<5 min), H2 purities higher than 95% are achieved, with CO2 purities near 0%.

Green hydrogen production from sorption-enhanced steam reforming of biogas over a Pd/Ni–CaO-mayenite multifunctional catalyst

The carbon-neutral application of biogas to produce “green hydrogen” appears to be an attractive solution to ensure the sustainability of energy production. However, the high and variable CO2 content in biogas has limited the development of biogas utilization. Herein, we report that sorption-enhanced steam reforming of biogas (SESRB) provides an efficient way to obtain high-purity hydrogen from biogas with the in-situ removal of CO2. The effect of temperature and CO2 content on CH4 conversion and H2 purity is studied. The results indicate that the content of CO2 does not affect the CH4 conversion and H2 purity in the pre-breakthrough stage of SESRB process. Meanwhile, the performance of long-term stability shows that 98.0 vol% H2 with ⁓97.8% conversion of CH4 in the pre-breakthrough stage is stably obtained over the Pd/Ni–CaO-mayenite-2.8 multifunctional catalyst for 30 SESRB-calcination cycles. The small amount of coke (0.8 wt%) formed during the SESRB reaction can be effectively eliminated by carbon gasification during calcination treatment. The results point out that SESRB is a promising technology for the efficient utilization of biogas to produce high-purity hydrogen.

Bifunctional Ni–CaO catalysts modified with CeO2 and inert Ca12Al14O33 for sorption-enhanced steam reforming of ethanol

In this work, sorption-enhanced steam reforming of ethanol (SE-SRE) process was studied using Ni–CaO-based bifunctional catalysts modified with Ca12Al14O33 (mayenite) and CeO2. The CaO and CaO/Ca12Al14O33 sorbents were synthesized by a sol-gel method and, subsequently, CeO2 and Ni were added by the incipient wetness impregnation method. These materials were characterized by BET surface area, thermogravimetric analysis (TGA), in situ X-ray diffraction (XRD), and in situ X-ray absorption near edge structuare (XANES). In addition, the catalysts were tested on 10 cycles of SE-SRE reaction and regeneration. In general, the characterization results revealed an inverse relationship between average crystallite size of CaO and CO2 sorption capacity. By the in situ XRD/XANES, the addition of the mayenite reduced by half the average crystallite size of CaO and increased the interaction between support and active phase. As a consequence, the catalyst containing mayenite (NiCaAl) showed the best CO2 capture uptake and stability, which could be justified mitigation of the CaO sintering effect by the inert material presence. Great stability was also observed in the catalytic tests, since the duration of the pre-breakthrough stage for NiCaAl and for the catalyst containing maynite and ceria (NiCaAlCe) remained constant over the reaction cycles. In terms of hydrogen production, NiCaAl catalyst showed the highest H2 molar fraction during the pre- (90%) and post-breakthrough. The CeO2 addition slightly favored the methane formation, although did not bring significant benefits in the CO2 capture and catalytic performance. Therefore, NiCaAl showed the best CO2 capture capacity and stability, which led to the best SE-SRE performance.

High-purity hydrogen production from phenol on Ni-CaO-Ca12Al14O33 multifunctional catalyst derived from recovered layered double hydroxide

Hydrogen production with in situ CO2 capture by the sorption-enhanced steam reforming (SESR) technology is a promising concept to reduce anthropogenic CO2 emissions. A serious disadvantage of SESR processes is the rapid, sintering-induced decay of its cyclic performance. Here, a recovery approach of Ni-Ca-Al layered double hydroxide (LDH) structure with adsorbed tetracycline to develop a multifunctional catalyst is exploited. The in situ formation of carbon template originating from the adsorbed tetracycline allows for the emergence of favorable structure possessing excess porosity along with deposition of small nanoparticles, thus providing physical isolation to inhibit the sintering of Ca and Ni species. As such, 98.3 vol% H2 was stably produced from phenol in 50 cyclic tests, during which only 33 % decrease of sorption-enhancement effect was observed, ensuring superior SESR of phenol performance. This strategy provides a new paradigm for the rational design of materials derived from LDH for high-temperature reactions.

Sorption-enhanced steam reforming of CH4/CO2 synthetic mixture representing biogas over porous Ni–CaO–MgO microsphere via a surface modified carbon template

Sorption-enhanced steam reforming of biogas (SESRB) provides an efficient way to obtain high-purity hydrogen from biogas. Highly effective bi-functional adsorbent/catalyst materials play a key role in the long-term operation of SESRB process. Here a general template-based approach using carbon microspheres with alkali modification (MCS) as sacrificial templates to synthesize highly effective bi-functional catalyst is reported. FT-IR, XPS and TGA confirm the enhanced adsorption capacity of MCS to metal ions due to the existence of rich oxygen containing functional groups. The amount of the obtained bi-functional catalyst is increased by 14 times after NaOH treatment. Electron microscopy analysis shows the uniformity of composition and the formation of a favorable morphology, including porous structure and separated nanoparticles, are the crucial for yielding high-performance bi-functional catalyst. Due to the excellent stability of the catalyst structure, 92.3 vol % of hydrogen (dry and inert-free gas basis) with 92% CH4 conversion is obtained over the 1Ni–CaMg6-M catalyst for 10 consecutive reaction-desorption cycles.