Promoting behaviors of alkali compounds in low temperature methanol synthesis over copper-based catalyst

Hybrid catalyst systems comprised of Na compounds (HCOONa, NaOH, Na2CO3 and NaHCO3) and Cu/MgO catalysts have contributed to a novel high-performance methanol synthesis in ethanol solvent from syngas (CO/H2 = 1/2) at a low temperature of 433 K and 5 MPa. It is found that Na2CO3 dopant is more beneficial to enhance hydrogenolysis ability of Cu/MgO catalyst than NaOH and HCOONa. Whereas, all the starting Na compounds in ethanol solvent are reversibly converted to HCOONa in alcohol solvent by ex situ observations, revealing that formate alone is the essential species in the catalytic circle. The results unambiguously elucidate that the essence of alkali component in promoting the low temperature methanol synthesis is virtually attributed to the formation of highly reactive alkali-participated active site. It is also proposed that solid Cu/MgO catalyst should play binary roles in successive carbonylation and hydrogenolysis reactions.