Towards High Efficacy of Pd-Au/C Catalyst for Tetrachloromethane Hydrodechlorination

Abstract

We present an efficient strategy for synthesising the PdAu catalysts with a homogeneous PdAu alloy phase for environmentally important hydrodechlorination of tetrachloromethane in the gas phase. The synthesis of carbon-supported catalysts involved two major steps: (i) incorporation of palladium and gold nanoparticles into carbon support and (ii) activation of the catalysts. The critical part of this work was to find the optimal conditions for both steps. Thus, the incorporation of the nanoparticles was carried out in two ways, by impregnation and direct redox reaction method using acetone solutions of metal precursor salts. The activation was performed either by a conventional thermal reduction in hydrogen or flash irradiation in a microwave oven. The homogeneity and structure of the PdAu alloy were found to depend on the catalyst activation method critically. In all cases, we observed better homogeneity for catalysts that were subject to microwave irradiation. Moreover, the flash microwave irradiation of prepared catalysts provided catalysts of better stability and selectivity towards the desired products (hydrocarbons) in the hydrodechlorination of tetrachloromethane as compared to the catalyst obtained by conventional thermal activation in hydrogen.

Supported nanocatalysts: recent developments in microwave synthesis for application in heterogeneous catalysis

“…Fair number of attempts have also been made to prepare supported simple metal oxide (CoO x , Co 3 O 4 , NiO, Fe 3 O 4 , SnO 2 , CeO 2 , TiO 2 ) nanocatalysts for application in petrochemical industry. 75,[160][161][162][163][164][165][166] In order to improve the catalytic activity as well as versatility in application potential of simple metal or metal oxide nanocatalysts, investigations on supported bimetal, [171][172][173][174][175][177][178][179][180][181][182][183][184][185][186][187] mixed metal oxide [188][189][190][191][192][193]196,197 and ternary metal 198,199 nanocatalysts are also available. MW assisted synthesis has been claimed to be economically viable short green method to produce supported nanocatalyst.…”

“…Independent of NPs incorporation methods (IM or DR), Pd-Au/C catalysts activated by MW irradiation exhibited better hydrodechlorination, HdCl, activity than those activated by thermal treatment in hydrogen. 174 The improved catalytic activity was attributed to better homogeneity in Pd-Al alloy. The deactivation for the PdAu-DR-MW catalyst was also the lowest owing to the best homogeneity of Pd-Au alloy phase.…”

“…107,116,128 A comparative study of MW assisted methods and conventional methods, whenever investigated, demonstrated that MW methods promoted fast nucleation, produced more homogeneous smaller size NPs within short time, improved catalyst loading and better alloying in binary/ternary metallic phase because of high loss tangent values, strong MW absorption, thus fast and rapid heating and lower activation energy. 112,118,120,121,136,138,139,160,162,163,174,184 The usefulness of MW assisted methods is dependent on the ability to produce perfectly homogeneous distribution of uniform nanosized catalyst with controlled morphology on the solid support. The intimate contact with strong fixation is also a desirable requirement from the view point of stability and well dispersity of nanocatalyst on the support.…”

“…Interestingly, in most cases the MW assisted synthesized supported nanocatalysts possessed better catalytic activity compared to the commercial 95,101,147,162,l86 and/or corresponding nanocatalyst prepared by other conventional methods. 118,120,121,136,139147,162,163,174 Though the comparative data on corresponding catalyst prepared by other conventional methods is still inadequate but it is reasonable to conclude on the basis of available results that MW assisted synthesized supported 55 nanocatalysts possessed good prospects for industrial use. Some authors even carried out the catalysis reactions under MW reaction conditions over supported nanocatalysts and found fairly good conversion and/or yield.…”

“…In some instances even better recycle stability was observed for MW assisted synthesized supported nanocatalysts. 118,164,174 Though the data on stability and recyclability of MW synthesized nanocatalyst is encouraging but much effort is necessary to further improve the performance, as in some cases the activity decreased significantly after few reaction cycles. 85,86,95,98,99,107,116,133,174 The decrease in activity during recycle in either case occurred mostly due to change in morphology, aggregation, graphitization and loss of active catalyst via leaching of metal ions.…”