Thermally Stable Alkylidene Groups on the Surface of β-Mo2C: Relevance to Methane Aromatization and Olefin−Metathesis Catalysis

Abstract

A combination of surface spectroscopy and chemical reactivity studies was used to show that alkylidene groups, formed on β-Mo2C through the dissociative adsorption of ketones, are stable under ultrahigh vacuum conditions to anomalously high temperatures. Results are presented for cyclobutylidene, cyclopentylidene, and cyclohexylidene. Reflectance absorbance infrared spectroscopy in the CH2 stretching region, high-resolution X-ray photoemission measurements, labeled oxygen insertion, and metathesis reactions were used to detect surface alkylidenes at or above 900 K. The anomalous thermal stability of alkylidenes on the carbide surface shows that carbenes may be present on the carbide phase of Mo/ZSM-5 catalysts during the methane dehydroaromatization reaction. The latter reaction is typically carried out at approximately 970 K.