Monomeric Copper(II) Sites Supported on Alumina Selectively Convert Methane to Methanol

Abstract

Monomeric CuII sites supported on alumina, prepared using surface organometallic chemistry, convert CH4 to CH3OH selectively. This reaction takes place by formation of CH3O surface species with the concomitant reduction of two monomeric CuII sites to CuI, according to mass balance analysis, infrared, solid‐state nuclear magnetic resonance, X‐ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH3OH exceeding 83 %, based on the number of electrons involved in the transformation. These alumina‐supported CuII sites reveal that C−H bond activation, along with the formation of CH3O‐ surface species, can occur on pairs of proximal monomeric CuII sites in a short reaction time.

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

“…This required the study of the reaction over the CuMOR(46) sample, which predominantly contains the Cu II ‐hydroxo monomeric species. It was recently shown that monomeric species are active in methane conversion and allows achieving higher selectivity with respect to that observed over the CuMOR(6) sample, which contains active sites with multiple copper atoms (see the Supporting Information) . Similar results were reproduced for our CuMOR(46) material (Table ).…”

Pathways of Methane Transformation over Copper‐Exchanged Mordenite as Revealed by In Situ NMR and IR Spectroscopy

“…It was recently shown that monomeric species are active in methane conversion and allows achieving higher selectivity with respect to that observed over the CuMOR(6) sample, which contains active sites with multiple copper atoms (see the Supporting Information). [24,65] Similar results were repro-Tabelle 2: Assignment of IR bands observed during the reaction of copper-exchanged mordenites with methane at elevated temperature. The deconvolution of the bands at 1458 and 1469 cm À1 due to the deformation vibrations of CH 3 group in methanol and methoxy species is complicated and the therefore the assignmentw as based on the literature data.…”

Comparative performance of Cu-zeolites in the isothermal conversion of methane to methanol

“…4,13,16,17 Within this stepwise procedure, much focus has been given to the nature of the active site with multiple different motifs proposed. 4,14,[18][19][20][21][22][23] In spite of multiple proposed active sites, these works agree that high activation temperature (4623 K) in oxygen is required to form the active sites which store the activated oxygen that will selectively convert methane to methanol. 4,14,24 It was assumed that a high temperature activation was required until a low-temperature, isothermal, procedure was introduced where the activation and reaction are conducted at 473 K but with an elevated pressure of methane to boost the methanol yield.…”