Effect of calcination temperature on Co/sepiolite catalyst for hydrogen production by ethanol steam reforming: Co speciation from phyllosilicate to spinel

Hydrogen production via ethanol steam reforming (ESR) was conducted over amorphous sepiolite (SEP) supported Co based catalysts, deeming as a green and sustainable strategy for renewable energy. However, the subtle regulation to the ESR reactivity of Co/SEP catalysts still remains a challenge. Given the structure sensitive property of ESR, calcination temperature, as a vital regulation parameter, was used to control the key physicochemical properties of catalysts. By various characterization techniques, the results revealed that a calcination temperature mediated metal-support interaction was manifested in the form of Co speciation evolution. With increasing calcination temperature, the occurrence states of Co species change from Co oxides to Cophyllosilicate then to Co-Al spinel. The ESR experiments indicated that Co/SEP-600 catalyst possessed a suboptimal activity via a dehydrogenation route and a 50 h stability due to a compromising among Co-phyllosilicate dominated MSI, texture, Co0 nanoparticle size and acid-base property. The further improvement of calcination temperature only brought about a poor stability of Co/SEP-700 with a phase transformation or a low activity of Co/SEP-800 with an irreducible Co-Al spinel. Hence, the interaction type of Co with SEP framework Si/Al atoms determined the ESR reactivity of the catalysts, which was modulated by the calcination temperature. Additionally, abundant graphitic coke deposition on the agglomerated Co0 grains was attributed the weak MSI, such as Co/SEP-400, while a slight coke deposition appeared at Co/SEP-800 with an irreducible Co-Al spinel phase.