Greatly changed performance of a metal Pd catalyst by a rather easily formed and removed species–PdHx
Pd catalysts, which are often prepared by reducing Pd salts with NaBH4, have been intensely studied in HCOOH dehydrogenation (FAD) for H2 production. FAD can also be used to hydrogenate or reduce various chemicals by using its in situ generated hydrogen, which exhibits superiority over the direct use of H2 gas. Herein, by using FAD to reduce Cr(VI) as a room-temperature probe reaction, we show that some Pd atoms in the catalyst form PdHx under normal conditions during both catalyst preparation and catalytic reaction (NaBH4 or HCOOH as a hydrogen donor). PdHx greatly hinders Cr(VI) reduction and, interestingly, boosts H2 generation. That is to say, PdHx can be negative or positive species, depending on the focused product. The reason for this phenomenon was also analyzed. Heat treatment for only 10 min can destroy PdHx species and thus, improve the activity for Cr(VI) reduction by up to ∼3 times, which is effective in each catalyst reuse. These findings are critical for controlling the design and functioning of Pd catalyst.
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