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

• DFT and microkinetic modeling were performed to study the mechanism of the propane dehydrogenation over Pd(100), Pd(210), Pd 3 Bi 1 (100), Pd 2 Bi 1 (100), Pd 1 Bi 1 (100), and Pd 1 Bi 1 (210). • With the increase of the Bi concentration, the ε d of the surface layer moves to the lower energy, and the propylene bonding strength decreases. AIMD finds the temperature at which propylene begins to desorb also decreases. • Two selectivity descriptors (Δ E selec, 1 and Δ E selec,2) succeed in predicting the propylene selectivity on the pure Pd and Pd-Bi intermetallic compounds, because the barriers for both C-C crack and propylene deep dehydrogenation approximately increase with Bi concentration. • Under typical reaction conditions, the apparent activation energies are 1.04, 1.34, 1.78, and 2.07 eV on the Pd(100), Pd 3 Bi 1 (100), Pd 2 Bi 1 (100), and Pd 1 Bi 1 (100), respectively. And the propylene selectivity increases from 0.64 on the Pd(100) to 0.99 on the Pd 1 Bi 1 (100). • The isolated Pd sites on the Pd 1 Bi 1 (100) and Pd 1 Bi 1 (210) result in a relatively high e a eff for propane dehydrogenation and a lower TOF of propylene. As a compensation between activity and selectivity, the Pd 2 Bi 1 (100) may be more suitable for PDH. 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 SiO 2. The Pd-Bi/SiO 2 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), Pd 3 Bi 1 (100), Pd 2 Bi 1 (100), Pd 1 Bi 1 (100), Pd(210), and Pd 1 Bi 1 (210). Due to the isolated Pd sites, Pd 1 Bi 1 (100) and Pd 1 Bi 1 (210) showed the highest propylene selectivity but low TOF of propylene. The Pd 2 Bi 1 (100) may be more suitable for PDH because of the compensation between activity and selectivity. Two selectivity descriptors (Δ E selec, 1 and Δ E selec, 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 Δ E selec, 1 and Δ E selec, 2 succeed in predicting the propylene selectivity on the pure Pd and Pd-Bi catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]