(638g) N-Butane to 1,3-Butadiene Reaction over Pt Single Atoms in ZnOx Nests in Dealuminated Zeolite Beta

As an important chemical intermediate in industrial polymer manufacture, 1,3-butadiene (1,3-BD) is conventionally produced from steam cracking of naphtha. Recently, an on-purpose alternative using n-butane sourced from the liquid fraction of shale gas to produce 1,3-BD has attracted researchers’ interests. In the propane and ethane dehydrogenation reactions, Pt nanoclusters and Pt single atoms have been found and proved as efficient catalysts, while much less is known about their activity for the dehydrogenation of n-butane to 1,3-BD. In this study, atomically distributed Pt sites confined in ZnO_x nests crated in dealuminated zeolite Beta (DeAlBEA) were synthesized and characterized with atomic-resolution STEM, XANES, EXAFS as well as ¹H and ²⁹Si SQ-DQ NMR. As revealed, isolated Pt⁴⁺ in ZnO_x nests are formed in as-synthesized sample, which further transformed to PtZn intermetallic complexes with structure of (≡Si-O-Zn)₆Pt upon heating at 823 K. The reaction of n-butane to 1,3-BD carried out at 823 K and a WHSV = 14.5 h^-1 produced a 1,3-BD with a turnover frequency of 0.49 mol (mol Pt)^-1 s^-1, which is 21 times higher than that reported previously for PtZn catalyst. Both dehydrogenation of n-butane and 1-butene exhibit a Langmuir dependence on n-butane and 1-butene partial pressure, the rates increase linearly at low partial pressures but then decrease to less than first order at higher n-butane and 1-butene partial pressure. Space time studies and measurements of the kinetics of proposed intermediates suggest that n-butane first undergoes dehydrogenation to 1-butene, followed by rapid equilibration to 2-butene. 1-Butene then goes through secondary dehydrogenation to produce 1,3-BD. The hydrogenation of n-butenes and 1,3-BD back to n-butane or n-butenes are also observed.