Low-temperature fabrication of potassium single-atom solid base catalysts with high activity in transesterification

Abstract

Solid base catalysts are appealing to a variety of reactions due to their benefits of easy separation, negligible corrosion, and environmental friendliness. However, their activity is compromised because high temperature is frequently required for the formation of basic sites and aggregation of basic components is easy to occur under those circumstances. Herein, K single-atom solid base catalysts were fabricated by a low temperature, pyrolysis-free, grafting strategy, resulting in the catalysts with highly dispersed basic sites and high activity in transesterification reaction. Potassium tert-butoxide (KTB) functions as the precursor and mesoporous silica SBA-15 is employed as the support, K atoms are successfully grafted onto SBA-15 (denoted as K1/SBA-15) at 30 °C. Various characterizations confirm that highly dispersed K single atoms exist in the form of K-O-Si. The amount of basic sites of K1/SBA-15 measured by titration is 1.62 mmol·g−1, verifying the basicity of the obtained catalyst. K1/SBA-15 shows excellent activity (49.1 % yield) in the transesterification reaction of ethylene carbonate (EC) and methanol to produce dimethyl carbonate (DMC), which is superior to typical alkali metal-related solid superbases. The catalyst was recovered after reaction and the yield of DMC over the recovered catalyst decreases slightly (43.4 %) due to the partial deformation of pores. Moreover, the K1/SBA-15 exhibits a turnover frequency (TOF) value of 82.5 h−1, obviously higher than various reported solid base catalysts (0.95–36.2 h−1) under semblable reaction conditions.