Carbonate vacancy-engineered K/K2CO3 solid superbases achieve exceptional selectivity via enhanced metal-support interactions in sustainable isobutene dimerization

Achieving the selective catalytic dimerization of the branched olefin via solid superbases remains a challenging yet sustainable strategy. In this study, a series of K/K 2 CO 3 solid superbase catalysts were rapidly prepared via the melt-loading method for the dimerization of isobutene (IBE) to 2,4,4-trimethyl-1-pentene (TP1). Carbonate vacancy concentration was readily tuned by regulating the pretreatment temperature of K 2 CO 3 . The screened 5%K/K 2 CO 3 -430°C catalyst, containing an appropriate amount of carbonate vacancies, achieved an isobutene conversion of 49.8% and a TP1 selectivity exceeding 80.9% under mild conditions (190 °C, 15 h), significantly outperforming conventional solid acid catalysts. Characterization results demonstrate that the carbonate vacancies (anion lattice defects) induced by optimal pretreatment temperature generate more coordinatively unsaturated oxygen (CUO) sites on the surface. These sites substantially strengthen the metal-support interaction (MSI, in a broad sense) between K and K 2 CO 3 , thereby enhancing the electron-donating ability of the superbasic sites. DFT calculations further reveal that the loaded metallic K promotes electron transfer to IBE through electron density redistribution and the semi-encapsulation configuration of K atoms in tri-oxygen hollow sites, enabling efficient activation of isobutene. In situ DRIFTS detects allylic anion intermediates, confirming that the reaction proceeds via a radical-anion pathway. This study provides a facile and effective approach for the efficient preparation of solid superbases and the construction of defect engineering in catalysts, offering new insights into the design of high-performance catalysts for green olefin conversion.