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 CO 2 hydrogenation into dimethyl ether (DME), whereby it consists of Pd/In 2 O 3 for CO 2 hydrogenation into methanol, and H-ZSM-5 for methanol dehydration into DME. The catalyst development was focused on the synthesis of Pd/In 2 O 3 via a green and low-cost synthesis method of carbonized alginate templating. Thus, microspherical-confined nano-Pd/In 2 O 3 was formed, whereby the localized nucleation growth was coordinated by the chemically entrapped In 3+ 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 °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/In 2 O 3 : H-ZSM-5 (PdIn-160–12: H-ZSM-5) mass ratio of 4:1, the highest STY DME of 79.7 g DME kg cat -1 h −1 with CO 2 conversion of 9% and DME selectivity of 44.1% can be achieved. In addition, the STY DME can be maintained even in 60 h on stream, demonstrating the excellent stability and performance of microspherical-confined nano-Pd/In 2 O 3 /H-ZSM-5 bifunctional catalyst synthesized via carbonized alginate templating strategy.