Highly active and durable Ca-based solid base catalyst for biodiesel production

• A novel solid-state synthesis approach to fabricate the Ca-based solid base catalyst. • NCS catalyst has strong basic sites and performs excellent in transesterification. • NCS catalyst could be reused 27 times without significant deactivation. • NCS’s stability owes mainly to the coordination between Ca and assistive components. Calcium-based (Ca-based) oxides are promising candidates to replace sodium or potassium hydroxide as base catalysts in transesterification for biodiesel production, owe to their high activity and recyclability. However, their readily leaching in the reaction process is the main reason for its low reusability. This problem has long been the bottleneck of heterogeneous catalytic transesterification for biodiesel production. To solve this problem, we employed a solid-state synthesis approach to fabricate the Ca-based solid base catalyst, which showed extraordinarily high activity and stability for biodiesel synthesis. The catalyst, named NCS, could achieve up to 98.0% biodiesel (fatty acid methyl esters, FAMEs) yield in 1 h at 90 °C with 5 wt% of catalyst loading. The catalyst can be reused 26 times with a biodiesel yield of at least 90.0%. With thorough characterization, we found that the extraordinary performance of the catalyst owes to the strong basic sites and its anti-carbonation ability. The strong basic sites, formed by the coordination between O, Na, Si, and Ca, can also moderate the leaching of Ca-related basic sites into the reaction medium. Performance reduction of NCS could be attributed to the shift of strong basic sites to weaker ones without significant loss of total basic sites. Above all, we believe that the NCS catalyst is a promising catalyst for large-scale biodiesel production.