Synergistic Lewis acid and Pd active sites of metal–organic frameworks for highly efficient carbonylation of methyl nitrite to dimethyl carbonate

Abstract

Metal–organic frameworks (MOFs) have recently been applied as versatile platforms for constructing efficient catalysts with improved performance in many fields. Herein, for the first time, we prepare a MOF UiO-66 based catalyst showing the synergistic effect of Lewis acid and Pd(II) active sites, and it shows highly efficient methyl nitrite (MN) carbonylation to dimethyl carbonate (DMC). Lewis acid sites were first introduced to UiO-66 by adding different amounts of trifluoroacetic acid (TFA) and activating at different temperatures. Pd(II) sites were then supported on UiO-66_x-X to obtain the resulting Pd-UiO-66_x-X (x, the molar percentage of TFA; X, activation temperature). The Lewis acid sites not only act as the center of CO adsorption, but affect the electron density of Pd(II) for the generation of more COOCH₃* intermediates, resulting in a higher catalytic performance. As a result, the best catalytic performance based on the DMC selectivity based on CO (S_DMC/CO) near 100%, S_DMC/MN up to 67.4%, CO conversion to DMC (C_CO) as high as 68.4%, and the weight time yield (WTY) of DMC up to 2056 g kg_cat⁻¹ h⁻¹ was achieved by the composite material Pd-UiO-66_TFA-0.25-290. This work provides efficient catalysts for carbonylation of MN to DMC and presents a significant synergistic methodology for improving the catalytic performance of MOF materials.