Development of an effective bi-functional Ni-CaO catalyst-sorbent for the sorption-enhanced water gas shift reaction through structural optimization and the controlled deposition of a stabilizer by atomic layer deposition

The integration of a CaO-based CO 2 sorbent into catalytic schemes to remove CO 2 from the product stream provides an effective means to reduce greenhouse gas emissions of chemical processes and to improve the yield and purity of the desired product. A key requirement for such so-called sorbent-enhanced processes is the availability of cyclically stable CO 2 sorbent. To this end, we have developed CaO-based CO 2 sorbents that combine favourable structural features and a high thermal stability by introducing a thin, conformal layer of Al 2 O 3 (forming Ca 3 Al 2 O 6 with CaO upon calcination) by atomic layer deposition. The structure and pore volume of the sorbent were found to play a key role in its CO 2 capture. Functionalizing such CO 2 sorbents with Ni nanoparticles yielded a highly effective bi-functional material for the sorption-enhanced water-gas shift (SE-WGS) reaction. The material showed a high yield of hydrogen of high purity and minimal CO slip over several cycles of repeated SE-WGS/regeneration operation. Bi-functional Ni-hollow CaO stabilized by ALD-grown Al 2 O 3 overcoat for sorption-enhanced water-gas shift reaction producing high purity hydrogen.