Novel CaO–SiO₂ Sorbent and Bifunctional Ni/Co–CaO/SiO₂ Complex for Selective H₂ Synthesis from Cellulose

Abstract

Catalysis- and sorption-enhanced biomass gasification is a promising route to high-purity hydrogen (H₂); however, most CaO-based sorbents for CO₂ capture have poor surface area and mechanical properties, lose carrying capacity over multiple uses, and have insufficient porosity to accommodate extra catalyst sites. We aimed to develop a high-surface-area CaO–SiO₂ framework onto which catalysts could be grafted. The best CaO–SiO₂ sorbent (<i>n</i>_Ca/<i>n</i>_Si = 2:1) maintained a CaO conversion of 65% even after 50 carbonation–decarbonation cycles, better than commercial micrometer-sized CaO or tailored CaO, because of stabilization via Ca–O–Si interactions and an ordered porous structure. Bimetallic catalyst grains (Ni/Co alloy, <20 nm) could be evenly loaded onto this structure by impregnation. The resulting bifunctional complex produced H₂ at nearly the same rate as a mixture of catalyst and commercial CaO while using less total sorbent/catalyst. Furthermore, this complex was much more durable due to its higher coking resistance and stable structure. After 25 carbonation–decarbonation cycles, the new catalyst–sorbent complex enhanced the H₂ yield from cellulose far more than a mixture of catalyst and commercial CaO did following the same treatment