Experimental and theoretical study unveiling the role of solvents on CO activation and hydrogenation to methanol in three-phase reactor system

Abstract

Syngas conversion to methanol in the slurry reactor is a developing technology where selecting suitable solvent is a crucial step. The activity test were performed in the stirred tank slurry reactor at 240 °C, 50 bar, 1000 rpm with three different solvents (paraffin, diglyme and DMSO) with CuZnO (CuO:ZnO = 40:60 by weight) catalyst to solely study the role of solvents. In the presence of the diglyme more CO conversion and methanol selectivity was obtained than paraffin and DMSO. Further, the CO adsorption on Cu(111) is calculated by DFT combined with the Conductor like Screening Model (COSMO) model to study the solvent effect. CO activation and stability have been studied by analyzing surface energy, adsorption energy, Mulliken charges of CO and Cu (111), Partial density of states (PDOS), sigma profiles, and dipole moment of the free CO in solvents. PDOS peaks of free CO shifted towards Fermi level in the presence of solvents which highlights the role of solvents in CO adsorption on Cu(111). Sigma profiles uncover facile CO adsorption on the hollow sites of Cu (111) facet in the presence of the solvent. Surface energy of the Cu(111) in different solvents are calculated which signifies the more surface area exposure in the presence of diglyme. The experimental results validated by the theoretical results revealing the role of moderate polarity in CO hydrogenation. This work will provide insight on the potential solvent selection for the methanol synthesis in a slurry reactor.