Al-free Zr-beta zeolite as a selective catalyst for the ketalization of glycerol

Abstract

Two Zr-beta zeolites were synthesized using different methods. Method 1 consisted in the formation of a dealuminated zeolite beta seed followed by Zr incorporation and thermal treatment (ZBZr1). In Method 2, zeolite beta was prepared and then, the dealumination and subsequent Zr incorporation were performed (ZBZr2). These materials were tested in the ketalization of glycerol with acetone and compared with a SBAsulf. Both preparation methods incorporate Zr in the zeolitic framework, and no ZrO2 is detected. Method 1 developed crystallites with an average size of 260 nm, Si/Zr ratio ∼100, total amount of acid sites of 0.375 mmol.g−1 and a ratio of Brönsted to Lewis acid sites of 1.9. In the case of Method 2, values of 1500 nm, ∼86, 0.32 mmol.g−1 and 0.7 were obtained, respectively. The ZBZr2 sample presented low catalytic activity, possibly due to diffusion limitations. The turnover frequency (TOF) was calculated as 44.84 and 60.37 min−1 for ZBZr1 and SBAsulf, respectively. After one cycle of reaction, both ZBZr1 and SBAsulf showed a decrease in the glycerol conversion, however, the selectivity remained constant in the ZBZr1 material after the reaction cycle and the catalytic activity could be reestablished after a thermal treatment.