High-purity hydrogen via the sorption-enhanced steam methane reforming reaction over a synthetic CaO-based sorbent and a Ni catalyst

Prediction of Combined Sorbent and Catalyst Materials for SE-SMR, Using QSPR and Multitask Learning

The process of sorption enhanced steam methane reforming (SE-SMR) is an emerging technology for the production of low carbon hydrogen. The development of a suitable catalytic material, as well as a CO₂ adsorbent with high capture capacity, has slowed the upscaling of this process to date. In this study, to aid the development of a combined sorbent catalyst material (CSCM) for SE-SMR, a novel approach involving quantitative structure–property relationship analysis (QSPR) has been proposed. Through data-mining, two databases have been developed for the prediction of the last cycle capacity (g_CO2/g_sorbent) and methane conversion (%). Multitask learning (MTL) was applied for the prediction of CSCM properties. Patterns in the data of this study have also yielded further insights; colored scatter plots were able to show certain patterns in the input data, as well as suggestions on how to develop an optimal material. With the results from the actual vs predicted plots collated, raw materials and synthesis conditions were proposed that could lead to the development of a CSCM that has good performance with respect to both the last cycle capacity and the methane conversion.

Experimental Characterization and Energy Performance Assessment of a Sorption-Enhanced Steam–Methane Reforming System

The production of blue hydrogen through sorption-enhanced processes has emerged as a suitable option to reduce greenhouse gas emissions. Sorption-enhanced steam–methane reforming (SESMR) is a process intensification of highly endothermic steam–methane reforming (SMR), ensured by in situ carbon capture through a solid sorbent, making hydrogen production efficient and more environmentally sustainable. In this study, a comprehensive energy model of SESMR was developed to carry out a detailed energy characterization of the process, with the aim of filling a current knowledge gap in the literature. The model was applied to a bench-scale multicycle SESMR/sorbent regeneration test to provide an energy insight into the process. Besides the experimental advantages of higher hydrogen concentration (90 mol% dry basis, 70 mol% wet basis) and performance of CO2 capture, the developed energy model demonstrated that SESMR allows for substantially complete energy self-sufficiency through the process. In comparison to SMR with the same process conditions (650 °C, 1 atm) performed in the same experimental rig, SESMR improved the energy efficiency by about 10%, further reducing energy needs.

Multishelled CaO Microspheres Stabilized by Atomic Layer Deposition of Al2 O3 for Enhanced CO2 Capture Performance

CO₂ capture and storage is a promising concept to reduce anthropogenic CO₂ emissions. The most established technology for capturing CO₂ relies on amine scrubbing that is, however, associated with high costs. Technoeconomic studies show that using CaO as a high-temperature CO₂ sorbent can significantly reduce the costs of CO₂ capture. A serious disadvantage of CaO derived from earth-abundant precursors, e.g., limestone, is the rapid, sintering-induced decay of its cyclic CO₂ uptake. Here, a template-assisted hydrothermal approach to develop CaO-based sorbents exhibiting a very high and cyclically stable CO₂ uptake is exploited. The morphological characteristics of these sorbents, i.e., a porous shell comprised of CaO nanoparticles coated by a thin layer of Al₂ O₃ (<3 nm) containing a central void, ensure (i) minimal diffusion limitations, (ii) space to accompany the substantial volumetric changes during CO₂ capture and release, and (iii) a minimal quantity of Al₂ O₃ for structural stabilization, thus maximizing the fraction of CO₂ -capture-active CaO.

Enhanced Hydrogen Production from Sawdust Decomposition Using Hybrid-Functional Ni-CaO-Ca2SiO4 Materials

A hybrid-functional material consisting of Ni as catalyst, CaO as CO₂ sorbent, and Ca₂SiO₄ as polymorphic "active" spacer was synthesized by freeze-drying a mixed solution containing Ni, Ca and Si precursors, respectively, to be deployed during sawdust decomposition that generated gases mainly containing H₂, CO, CO₂ and CH₄. The catalytic activity showed a positive correlation to the Ni loading, but at the expense of lower porosity and surface area with Ni loading beyond 20 wt %, indicating an optimal Ni loading of 20 wt % for Ni-CaO-Ca₂SiO₄ hybrid-functional materials, which enables ∼626 mL H₂ (room temperature, 1 atm) produced from each gram of sawdust, with H₂ purity in the product gas up to 68 vol %. This performance was superior over a conventional supported catalyst Ni-Ca₂SiO₄ that produced 443 mL H₂ g-sawdust^-1 under the same operating condition with a purity of ∼61 vol %. Although the Ni-CaO bifunctional material in its fresh form generated a bit more H₂ (∼689 mL H₂ g-sawdust^-1), its cyclic performance decayed dramatically, resulting in H₂ yield reduced by 62% and purity dropped from 73 to 49 vol % after 15 cycles. The "active" Ca₂SiO₄ spacer offers porosity and mechanical strength to the Ni-CaO-Ca₂SiO₄ hybrid-functional material, corresponding to its minor loss in reactivity over cycles (H₂ yield reduced by only 7% and H₂ purity dropped from 68 to 64 vol % after 15 cycles).

Iron-Doped BaMnO3 for Hybrid Water Splitting and Syngas Generation

A rationalized strategy to optimize transition-metal-oxide-based redox catalysts for water splitting and syngas generation through a hybrid solar-redox process is proposed and validated. Monometallic transition metal oxides do not possess desirable properties for water splitting; however, density functional theory calculations indicate that the redox properties of perovskite-structured BaMn_x Fe_1-x O_3-δ can be varied by changing the B-site cation compositions. Specifically, BaMn_0.5 Fe_0.5 O_3-δ is projected to be suitable for the hybrid solar-redox process. Experimental studies confirm such predictions, demonstrating 90 % steam-to-hydrogen conversion in water splitting and over 90 % syngas yield in the methane partial-oxidation step after repeated redox cycles. Compared to state-of-the-art solar-thermal water-splitting catalysts, the rationally designed redox catalyst reported is capable of splitting water at a significantly lower temperature and with ten-fold increase in steam-to-hydrogen conversion. Process simulations indicate the potential to operate the hybrid solar-redox process at a higher efficiency than state-of-the-art hydrogen and liquid-fuel production processes with 70 % lower CO₂ emissions for hydrogen production.

Tailor-Made Core-Shell CaO/TiO2-Al2O3 Architecture as a High-Capacity and Long-Life CO2 Sorbent

CaO-based sorbents are widely used for CO2 capture, steam methane reforming, and gasification enhancement, but the sorbents suffer from rapid deactivation during successive carbonation/calcination cycles. This research proposes a novel self-assembly template synthesis (SATS) method to prepare a hierarchical structure CaO-based sorbent, Ca-rich, Al2O3-supported, and TiO2-stabilized in a core-shell microarchitecture (CaO/TiO2-Al2O3). The cyclic CO2 capture performance of CaO/TiO2-Al2O3 is compared with those of pure CaO and CaO/Al2O3. CaO/TiO2-Al2O3 sorbent achieved superior and durable CO2 capture capacity of 0.52 g CO2/g sorbent after 20 cycles under the mild calcination condition and retained a high-capacity and long-life performance of 0.44 g CO2/g sorbent after 104 cycles under the severe calcination condition, much higher than those of CaO and CaO/Al2O3. The microstructure characterization of CaO/TiO2-Al2O3 confirmed that the core-shell structure of composite support effectively inhibited the reaction between active component (CaO particles) and main support (Al2O3 particles) by TiO2 addition, which contributed to its properties of high reactivity, thermal stability, mechanical strength, and resistance to agglomeration and sintering.

Biogas dry reforming for syngas production: catalytic performance of nickel supported on waste-derived SiO2

Waste-derived SiO₂ was used as catalyst support in the biogas dry reforming process, which showed a high catalytic activity and good stability.

Effect of pelletization and addition of steam on the cyclic performance of carbon-templated, CaO-based CO2 sorbents

In this work, we report the development of a synthetic CO2 sorbent that possesses a high cyclic CO2 uptake capacity and, in addition, sufficient mechanical strength to allow it to be used in fluidized-bed reactors. To overcome the problem of elutriation of the original powdered material, the synthetic CO2 sorbent was pelletized. An important aspect of this work was to assess the effect of steam on the cyclic CO2 capture capacity of the original, powdered CO2 sorbent and the pelletized material. After 30 cycles of repeated calcination and carbonation reactions conducted in a fluidized bed, the CO2 uptake of the pellets was 0.29 g of CO2/g of sorbent, a value that is 45% higher than that measured for the reference limestone. For the case that carbonation/calcination cycles were conducted in a thermogravimetric analyzer under steam-free carbonation conditions, the CO2 uptake of the best sorbent was 0.33 g of CO2/g of sorbent (after 10 cycles). Importantly, it should be noted that, after 10 cycles using wet carbonation conditions, the CO2 uptake of this material increased by 55% when compared to dry conditions. This observation was attributed to enhanced solid-state diffusion in the CaCO3 product layer under wet conditions. However, independent of the reaction conditions, the pelletized material showed a lower cyclic CO2 uptake when compared to the original powder. A detailed morphological characterization of the pellets indicated that the destruction of the primary, hollow micrometer-sized spheres during pelletization was responsible for the lower cyclic CO2 uptake of the pellets.

CaO-based CO2 sorbents: from fundamentals to the development of new, highly effective materials

The enormous anthropogenic emission of the greenhouse gas CO2 is most likely the main reason for climate change. Considering the continuing and indeed growing utilisation of fossil fuels for electricity generation and transportation purposes, development and implementation of processes that avoid the associated emissions of CO2 are urgently needed. CO2 capture and storage, commonly termed CCS, would be a possible mid-term solution to reduce the emissions of CO2 into the atmosphere. However, the costs associated with the currently available CO2 capture technology, that is, amine scrubbing, are prohibitively high, thus making the development of new CO2 sorbents a highly important research challenge. Indeed, CaO, readily obtained through the calcination of naturally occurring limestone, has been proposed as an alternative CO2 sorbent that could substantially reduce the costs of CO2 capture. However, one of the major drawbacks of using CaO derived from natural sources is its rapidly decreasing CO2 uptake capacity with repeated carbonation-calcination reactions. Here, we review the current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics. Subsequently, recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.