Reactivity of a Carbon-Supported Single-Site Molybdenum Dioxo Catalyst for Biodiesel Synthesis

A single-site molybdenum dioxo catalyst, (O c ) 2 Mo( ═ O) 2 @C, was prepared via direct grafting of MoO 2 Cl 2 (dme) (dme = 1,2-dimethoxyethane) on high-surface-area activated carbon. The physicochemical and chemical properties of this catalyst were fully characterized by N 2 physisorption, ICP-AES/OES, PXRD, STEM, XPS, XAS, temperature-programmed reduction with H 2 (TPR-H 2 ), and temperature-programmed NH 3 desorption (TPD-NH 3 ). The single-site nature of the Mo species is corroborated by XPS and TPR-H 2 data, and it exhibits the lowest reported MoO x T max of reduction reported to date, suggesting a highly reactive Mo VI center. (O c ) 2 Mo( ═ O) 2 @C catalyzes the transesterification of a variety of esters and triglycerides with ethanol, exhibiting high activity at moderate temperatures (60–90 °C) and with negligible deactivation. (O c ) 2 Mo( ═ O) 2 @C is resistant to water and can be recycled at least three times with no loss of activity. The transesterification reaction is determined experimentally to be first order in [ethanol] and first order in [Mo] with Δ H ⧧ = 10.5(8) kcal mol –1 and Δ S ⧧ = −32(2) eu. The low energy of activation is consistent with the moderate conditions needed to achieve rapid turnover. This highly active carbon-supported single-site molybdenum dioxo species is thus an efficient, robust, and low-cost catalyst with significant potential for transesterification processes.