Cerium-promoted bi-functional hybrid materials made of Ni, Co and hydrotalcite for sorption-enhanced steam methane reforming (SESMR)

Abstract

Multifunctional hybrid materials are promising for high-purity hydrogen (H2) production via catalytic steam reforming coupled with low temperature on-site CO2 capture. In the present work, novel hybrid materials made of Ni, Co (in varying proportions of 0–40%) and hydrotalcite (HTlc) were synthesized. The steam reforming activity of Ni was complemented by the high water-gas-shift (WGS) activity of Co. These unpromoted materials were referred to as Ni10Co30/HTlc (or HM1) and Ni20Co20/HTlc (or HM2). Thereafter, these materials were promoted with Ce species to improve the basicity and thermal stability of the composite material. The promoted materials were designated as Ce2.5Ni10Co30/HTlc (or Ce-HM1) and Ce2.5Ni20Co20/HTlc (or Ce-HM2). These materials were employed for sorption-enhanced steam methane reforming (or SESMR). The promotion with Ce resulted in strongly basic sites for CO2 adsorption, and hence, improved H2 production. Especially, Ce-HM1 exhibited the highest breakthrough time (45 min) and adsorption capacity (1.74 mol CO2/kg sorbent), whereas Ce-HM2 exhibited a breakthrough time of 30 min and adsorption capacity of 1.51 mol CO2/kg sorbent, producing >90 mol% H2 at T = 773 K, P = 0.1 MPa, S/C = 6 mol/mol, and gas hourly space velocity or GHSV = 3600 mL/(g-h). High surface area and basicity of the promoted materials hindered coke formation and undesired reactions. Furthermore, with the improved catalytic activity and adsorption characteristics, these materials were stable and easily regenerable. When multi-cycle durability tests were performed for 25 cycles, it was found that both the promoted materials Ce-HM1 and Ce-HM2 remained stable for up to 21 and 16 cycles. Thus, promotion with Ce was valuable for producing pure H2.