Role of reduction temperature on nanosized silicalite-1 zeolite confined Pd cluster catalysts for oxidation of hydrogen isotopes

Abstract

Controllable nuclear fusion is a major breakthrough in the future energy field and an important way for mankind to pursue clean and sustainable energy. However, since the fusion reaction raw material tritium is radioactive (β decay, half-life is 12.43 years), the leakage of these hydrogen isotopes under accident conditions will bring the risk of explosion and cause radiation damage to human. Therefore, efficient removal of hydrogen isotopes leaked due to accidents is crucial to the safe operation of nuclear fusion and human health. This study utilizes the metal-support interaction effect to design a series of Pd catalysts for efficient catalytic oxidation of hydrogen isotopes. Using pure silicon zeolite as a carrier, Pd is confined in the channel structure using a ligand-stabilized in situ encapsulation method. The prepared catalyst has nanoscale dispersed metal clusters and has excellent hydrogen isotope catalytic oxidation performance. This study systematically explored the effects of catalyst post-treatment methods, reaction space velocity, and reaction temperature on the hydrogen isotope catalytic oxidation conversion rate. The results show that the catalyst can be fully reduced at 600 °C and can achieve a hydrogen isotope catalytic oxidation conversion rate of greater than 98 % (24,000 mL g–1 h–1) at 100 °C. The conversion rate for hydrogen is higher than 96 % under the same space velocity at 50 °C. After 35,360 min (∼24.5 d) of continuous testing and intermittent operation, the catalyst can also maintain a conversion rate of 99 % (100 °C, 24,000 mL g–1 h–1). A lower reduction temperature will leave some organic matter, which will coordinate and bond on the Pd clusters and thus affect the catalytic activity. Under the same conditions, the hydrogen conversion rate of the catalyst directly reduced at 400 °C was 14 % lower than that of reduction at 600 °C, which proves the criticality of the reduction temperature. This work demonstrates a systematic study of utilizing the confinement effect of molecular sieve pores to obtain Pd cluster catalysts and applying them to the oxidative removal of hydrogen isotopes. It focuses on exploring the impact of the direct reduction temperature of the catalyst on its performance, which may be useful for providing a certain reference for designing relevant catalysts in engineering applications.