1. Dissociative recombination of HCl+, H2Cl+, DCl+, and D2Cl+ in a flowing afterglow
Justin P Wiens, Thomas M Miller, Nicholas S Shuman, Albert A Viggiano J Chem Phys. 2016 Dec 28;145(24):244312. doi: 10.1063/1.4972063.
Dissociative recombination of electrons with HCl+, H2Cl+, DCl+, and D2Cl+ has been measured under thermal conditions at 300, 400, and 500 K using a flowing afterglow-Langmuir probe apparatus. Measurements for HCl+ and DCl+ employed the variable electron and neutral density attachment mass spectrometry (VENDAMS) method, while those for H2Cl+ and D2Cl+ employed both VENDAMS and the more traditional technique of monitoring electron density as a function of reaction time. At 300 K, HCl+ and H2Cl+ recombine with kDR = 7.7±2.14.5 × 10-8 cm3 s-1 and 2.6 ± 0.8 × 10-7 cm3 s-1, respectively, whereas D2Cl+ is roughly half as fast as H2Cl+ with kDR = 1.1 ± 0.3 × 10-7 cm3 s-1 (2σ confidence intervals). DCl+ recombines with a rate coefficient below the approximate detection limit of the method (≲5 × 10-8 cm3 s-1) at all temperatures. Relatively slow dissociative recombination rates have been speculated to be responsible for the large HCl+ and H2Cl+ abundances in interstellar clouds compared to current astrochemical models, but our results imply that the discrepancy must originate elsewhere.
2. 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 ACS Omega. 2018 Jun 20;3(6):6651-6659. doi: 10.1021/acsomega.8b00244. eCollection 2018 Jun 30.
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.
