Efficient Reduction of Selenite to Elemental Selenium by Liquid-Phase Catalytic Hydrogenation Using a Highly Stable Multiwalled Carbon Nanotube-Supported Pt Catalyst Coated by N-Doped Carbon.

A stable catalyst, Pt/carbon nanotube (CNT) coated with N-doped carbon (Pt/CNT@CN), was designed to reduce selenite (Se(IV)) in water to elemental selenium by liquid-phase catalytic hydrogenation. Commercial Pt/C, pristine Pt/CNT, and carbon-coated Pt/CNT (Pt/CNT@C) were used for benchmarking. The Pt particles in Pt/CNT@CN were completely embedded beneath the coatings to minimize leaching and were not easily accessible to Se(IV). However, Schottky-Mott-type metal-carbon junctions that activate H2 were formed on the coated catalyst, facilitating effective reduction of Se(IV). The initial activity of Pt/CNT@CN (900.5 mg L-1 gcat-1 h-1) was two times higher than that of commercial Pt/C (448.6 mg L-1 gcat-1 h-1). The commercial Pt/C and uncoated Pt/CNT lost their initial activities during reuse and were almost inactive after 10 cycles due to significant Pt leaching (>90%) during the reaction and acid-washing regeneration processes. Pt/CNT@CN maintained 33% of the initial activity after the first cycle and stabilized over the following 9 cycles due to effective protection of Pt particles by carbon coatings. After 10 cycles, the activity of Pt/CNT@CN was over 20 times higher than that of Pt/C and uncoated Pt/CNT. Overall, catalytic hydrogenation using carbon-coated-supported Pt catalysts is an effective and promising approach to remove Se(IV) in water.