B2O3@BPO4 sandwich-like hollow spheres as metal-free supported liquid-phase catalysts

Abstract

Supported liquid-phase catalysts (SLPCs) combine the advantages of homogenous liquid-phase catalysts and heterogeneous catalysis (e.g., controllability of active centers and efficient product–catalyst separation). Generally, SLPCs manifest as a liquid-phase catalyst film or droplet adsorbed onto the surface of a porous support, such as ionic liquid-phase catalysts. Here, we extend this idea and develop a solvent-free liquid-phase catalyst supported on hollow spheres. We report sandwich-like B2O3@BPO4 hollow spheres synthesized through a one-step template-free method. At reaction temperatures (>450 °C), melted B2O3 supported on the surface of BPO4 hollow spheres acts as a catalytically active species for the selective oxidative dehydrogenation of propane to propene, with an excellent productivity of 0.79 gC3H6 gcat−1 h−1 and a high stability at 550 °C. We also found a phenomenon of tertiary aggregation during the formation of this sandwich-like hollow sphere. Additionally, the kinetic experiments indicate oxygen activation on the B2O3@BPO4 surface and second-order rate dependence with respect to the partial pressure of propane. This work may open a new avenue for the design and construction of metal-free oxides used as high-temperature SLPCs.