Synthesis of Pd/SiO2 Catalysts in Various HCl Concentrations for Selective NBR Hydrogenation: Effects of H+ and Cl- Concentrations and Electrostatic Interactions

Tingting Cheng; Jian Chen; Aofei Cai; Jian Wang; Haiyan Liu; Yuandong Hu; Xiaojun Bao; Pei Yuan

doi:10.1021/acsomega.8b00244

Synthesis of Pd/SiO₂ Catalysts in Various HCl Concentrations for Selective NBR Hydrogenation: Effects of H⁺ and Cl^- Concentrations and Electrostatic Interactions

ACS Omega. 2018 Jun 20;3(6):6651-6659. doi: 10.1021/acsomega.8b00244. eCollection 2018 Jun 30.

Authors

Tingting Cheng¹, Jian Chen¹, Aofei Cai¹, Jian Wang¹, Haiyan Liu¹, Yuandong Hu², Xiaojun Bao^{2

2}, Pei Yuan^{2

3}

Affiliations

¹ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, #18 FuXue Road, Beijing 102249, China.
² College of Chemical Engineering, State Key Laboratory of Energy and Environmental Photocatalysis, Fuzhou University, #2 Xueyuan Road, Fuzhou 350116, China.
³ National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, #523 Gongye Road, Fuzhou 350002, China.

Abstract

A series of silica supported Pd (Pd/SiO₂) catalysts were prepared in various HCl concentrations (C _HCl) of the impregnation solution with different electrostatic interactions between Pd precursor and support, and their catalytic properties were evaluated by the selective hydrogenation of nitrile butadiene rubber (NBR). The results show that with the C _HCl increasing from 0.1 to 5 M, the particle size of Pd nanoparticles dramatically decreases from 24.2 to 5.1 nm and stabilizes at ∼5 nm when C _HCl is higher than 2 M. Using the catalysts prepared with a high C _HCl (>2 M), an excellent hydrogenation degree (HD) of ∼94% with 100% selectivity to C=C can be acquired under mild conditions. Interestingly, the HD could be remarkably increased from 65 to 92% by increasing only C _Cl ^- from 0.1 to 2 M with the addition of NaCl while keeping C _H ^₊ at 0.1 M. This is because PdCl₄ ^2- is the predominant existing form of precursor at high C _Cl ^_- , which has a strong electrostatic attraction with the positively charged support favorable for the formation of small-sized Pd nanoparticles over silica. Notably, Pd leaching behavior during the hydrogenation reaction is closely related to C _H ^₊ , and the higher the C _H ^₊ , the less Pd residues are detected in the hydrogenated NBR. Our contribution is to provide a facile strategy to synthesize effective and stable Pd/SiO₂ catalysts via adjusting the electrostatic interaction, which exhibits a high activity and selectivity for NBR hydrogenation.