Synergistic Activating Effect of Promoter and Oxidant in Single-step Conversion of Methane into Methanol over Tailored Polymer-Ag Coordination Complex

Abstract

Single-step conversion of methane to its oxygenated derivatives, such as methanol, is a challenging topic in C1 chemistry. The presence of Bronsted-acidic sites, N- and O-type chelating ligands, and noble metals are demonstrated to be essential criteria for effective catalysis of this reaction. Considering these criteria, a catalytic complex was tailored herein. Poly-D-glucosamine (Ch) was used as chelating ligand for Ag, to incorporate the robust redox properties of Ag(I). The prepared AgCh complex was characterized by techniques including solid-state H-1-NMR, FE-TEM, XANES, and XPS. Besides highlighting the utility of chelate complexation for providing new materials, this study elucidates the effects of the oxidant and promoters on the methane oxidation. The catalytic activity was tested for different oxidant combinations, including hydrogen peroxide, oxygen, and carbon dioxide. Of all of them, a mixture of hydrogen peroxide and oxygen showed the highest selectivity for oxidation of methane to methanol. Further, it was observed that the addition of 1-butyl-3-methylimidazolium chloride [BMIM]Cl-+(-) as a promoter to the hydrogen peroxide and oxygen-containing AgCh system could enhance methanol production. The methanol yield reached up to 3166 mu mol, representing an 18-fold yield increase and an 8-fold methane conversion increase when compared to the results (175 mu mol) without a promoter.