Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

Abstract

The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE≠int, which is the actual interaction energy between the deformed reactants in the transition state.

Design of MFI Type Aluminum- and Titanium-Containing Zeolites

“…The thermal dehydrogenation of propane by the reaction 9 produces PP (reaction 11; ∆H = −125.7 kJ/mol) with a low conversion, as compared to the destruction process by reaction 10, which proceeds with the formation of methane and ETH (reaction 12; ∆H = −67.5 kJ/mol) [16]. The prevailing formation of methane during the thermal cracking of P could be explained by the cleavage of the C-C bond requires significantly less energy (261.9 kJ/mol) than that one of the C-H bond (364.5 kJ/mol for the primary carbon atom) [159].…”

Density Functional Theory Study on the Nucleation and Growth of Ptn Clusters on γ-Al2O3(001) Surface

“…4 Later, theoretically, it was reported that the neutral clusters Pt 2 , Pt 3 , and Pt 4 can activate the first C–H bond of CH 4 with small barriers, accompanied by the breakage of the second C–H bond in CH 4 as the rate-determining step. 5−7 More recently, we have studied the competitive activation mechanism of C–H and C–C bonds in C 2 H 6 and/or C 3 H 8 catalyzed by the Pt n ( n = 1, 2, and 4) cluster 8−12 and explained why the C–H insertion product is experimentally observed while the C–C insertion product is not formed in observable quantity 8,9 and why both Pt 2 and Pt 4 clusters exhibit more promising catalytic performance toward C 2 H 6 activation compared with the Pt atom. 10,12 These experimental and theoretical studies emphasize that the size of transition-metal clusters plays an important role in the catalytic reactivity.…”

Sequential and/or Simultaneous Wet‐Impregnation Impact on the Mesoporous Pt/Sn/Zn/γ‐Al2O3 Catalysts for the Direct Ethane Dehydrogenation

“…Overall, the Pt/A catalyst was more active as to that of the support A. However, it has shown very high % selectivity of undesired reaction products due to the Pt attack on C-C bond [59]. This led to higher cracking of ethane to methane and coke formation.…”

“…This is because of highly dispersed mesoporous Pt particles at the outer surface of unhomogenized catalyst due to the sequential wet impregnation of Pt to Sn/A catalyst to obtain SnPt/A catalyst. The availability of highly dispersed mesoporous Pt in the unhomogenized catalyst led to the enhanced % conversion due to C-C cleavage rather due to C-H cleavage, mandatory for dehydrogenation of ethane [9,34,35,37,58,59].…”

“…However, in the case of the Pt/A and SnPt/A catalysts, the % selectivity of methane (undesired reaction product) gradually decreased with the increase in reaction temperature (see Figures 2(b), 2(e), and 3(a)). This could be due to the freely available Pt mesoporous particles because it is well established that Pt has higher tendency to C-C bond cleavage [9,34,35,37,58,59]. In other words, it is the least formation of potential active alloy phase(s) between Pt and Sn in the case of SnPt/A catalyst.…”