Catalysis in flow: Operando study of Pd catalyst speciation and leaching

Abstract

Highlights: A custom-made plug-flow reactor (PFR) was constructed for examining Pd catalysis  Leaching/reaction profiles of two Pd catalysts for the Suzuki-Miyaura reaction were established by filtration studies.  The PFR was used to examine catalyst activation and deactivation processes  Ethanol was found to affect the catalysts differently  Leaching and speciation of Pd along the catalyst bed has been observed for the very first time. Catal Today (Highlights

Effects of Cl on the reduction of supported PdO in ethanol/water solvent mixtures

“…In all cases, irrespective of the nature of the Pd precursor used, and in common with their Cl-free counterparts, the reduced Pd nanoparticles are found to be significantly contaminated by interstitial hydrogen, which appears to be intrinsic to the chemistry between the Pd and the solvent components [10][11][12].…”

“…To address this problem, we have initiated a programme study, using operando Quick Pd K-edge EXAFS (QEXAFS) to investigate the effect of a flowing ethanol-water mixture on a number of Pd catalysts, containing different phases and size distributions of Pd nanoparticles supported upon different dispersant materials [10][11][12]. Concurrently, We have also investigated the behaviour of polymer encapsulated (ENCAT™) Pd catalysts under the same conditions [13].…”

“…The continuous flow reactor and the overall experimental protocols followed in this study have been fully described elsewhere [10]. Briefly, the solvent used comprised of a 50:50 v/v mixture of H 2 O/EtOH.…”

Effect of retained chlorine in ENCAT™ 30 catalysts on the development of encapsulated Pd: insights from in situ Pd K, L3 and Cl K-edge XAS

“…As part of a wider program of research using timeresolved quick scanning EXAFS (QEXAFS) to understand the fundamental behaviour of supported Pd nanoparticles in environmentally acceptable solvents, we have recently established a number of solvent induced behaviours (size dependent reducibility of PdO, formation of PdH x species, and Pd particle growth) [11][12][13][14] that are all observed at low temperatures in mixtures of EtOH/H 2 O (50:50); a solvent mixture widely employed in Pd-catalysis and highly rated in "green" solvent selection guides [15][16][17][18][19][20].…”

Halide-Enhanced Catalytic Activity of Palladium Nanoparticles Comes at the Expense of Catalyst Recovery

“…Following reductive elimination, Pd 0 atoms are then redeposited on the NPs [8]. Analogous mechanisms are supported by several further studies [53][54][55]. Alternative suggestions involve Pd atom leaching without involvement of the aryl halide.…”