Deposition Chemistry of Cu[OCH(Me)CH2NMe2]2over Mesoporous Silica.

The deposition of an organic copper precursor Cu[OCHMeCH 2NMe 2] 2on the surface of mesoporous silica MCM-41 dehydrated at 773 K was studied under high-vacuum conditions by infrared spectroscopy combined with elemental analysis, X-ray absorption spectroscopy (XAS), thermogravimetric analysis (TG), temperature-programmed decomposition (TPD), and X-ray photoelectron spectroscopy (XPS). It is revealed that the copper precursor is chemically adsorbed on the surface of MCM-41 to form a stable surface copper complex (SC1) coordinated with two framework oxygen atoms by ligand exchange at temperatures below 423 K. The surface copper complex is easily decomposed into Cu(I) and Cu(0) via a successive two-step pathway upon heating at temperatures beyond 423 K. IR and TPD results indicate that the first-step decomposition occurs at the temperature range from 423 to 523 K, where the surface complex SC1 loses one organic ligand and one methane molecule, leading to formation of a surface intermediate complex (SC2) with a Schiff base ligand. The second-step decomposition starts at 523 K, where the complex (SC2) is transformed to Cu(0) by losing the remanent organic ligand and undergoes a surface intermediate complex (SC3) to form Cu(I) oxide species by a consecutive loss of small molecules. The surface hydroxyl groups participate in the adsorption and reaction of the Cu precursor on the support MCM-41, which is a critical factor to controllable preparation of copper-containing MCM-41 catalysts. The mechanisms of thermolysis are suggested to be distinctly different from its MOCVD pathways reported in the literature. [ABSTRACT FROM AUTHOR]