Green synthesis of microspherical-confined nano-Pd/In2O3 integrated with H-ZSM-5 as bifunctional catalyst for CO2 hydrogenation into dimethyl ether: A carbonized alginate templating strategy

The present study developed bifunctional catalyst for CO2 hydrogenation into dimethyl ether (DME), whereby it consists of Pd/In2O3 for CO2 hydrogenation into methanol, and H-ZSM-5 for methanol dehydration into DME. The catalyst development was focused on the synthesis of Pd/In2O3 via a green and low-cost synthesis method of carbonized alginate templating. Thus, microspherical-confined nano-Pd/In2O3 was formed, whereby the localized nucleation growth was coordinated by the chemically entrapped In3+ via ionic bond in the well-distributed alginate structure. It was found that hydrothermal temperature plays a key role in the development of this catalyst structure. The optimum hydrothermal temperature is 160 degrees C, as it is able to produce the highest amount of methanol. This catalyst was further integrated with H-ZSM-5 via different integration manners. It was found that mortar mixed method produces the highest amount of DME, as the close proximity causes stronger ion-exchange mechanism between the catalyst components, which facilitates higher oxygen vacancy density in the bifunctional catalyst. Under the optimum Pd/In2O3: H-ZSM-5 (PdIn-160-12: H-ZSM-5) mass ratio of 4:1, the highest STYDME of 79.7 g(DME) kg(cat)(-1) h(-1) with CO2 conversion of 9% and DME selectivity of 44.1% can be achieved. In addition, the STYDME can be maintained even in 60 h on stream, demonstrating the excellent stability and performance of microspherical-confined nano-Pd/In2O3/H-ZSM-5 bifunctional catalyst synthesized via carbonized alginate templating strategy.