Propane dehydrogenation over Pd-Bi intermetallic compounds: A DFT combined with microkinetic modeling study

Abstract

Propylene is an important industrial raw material. The high temperature needed by the propane dehydrogenation (PDH) on the pure Pt or Pd catalyst may give rise to hydrogenolysis and carbon deposition, which ultimately poisons the catalysts. Experiments synthesized a series of Pd-Bi intermetallic compounds loaded on SiO2. The Pd-Bi/SiO2 catalyst with a moderate Bi concentration bears high activity and selectivity. But the reason is unknown. In the present paper, the DFT calculation and microkinetic modeling were performed to study the reaction network of PDH on the Pd(100), Pd3Bi1(100), Pd2Bi1(100), Pd1Bi1(100), Pd(210), and Pd1Bi1(210). Due to the isolated Pd sites, Pd1Bi1(100) and Pd1Bi1(210) showed the highest propylene selectivity but low TOF of propylene. The Pd2Bi1(100) may be more suitable for PDH because of the compensation between activity and selectivity. Two selectivity descriptors (ΔEselec,1 and ΔEselec, 2) could measure the influence of deep dehydrogenation and hydrogenolysis on the selectivity for propylene in the PDH, respectively. The barriers for both C-C crack and propylene deep dehydrogenation approximately increase with Bi concentration, which may be why both ΔEselec,1 and ΔEselec, 2 succeed in predicting the propylene selectivity on the pure Pd and Pd-Bi catalysts.