The effect of Pd‐catalyst wettability on hydrogenation of nitrate to hydroxylamine

In the HPO process of the DSM, nitrate is reduced to hydroxylamine on Pd/C catalyst in a 5 M salt solution. Pd/C catalyst increases the interfacial area by a coalescence hindering effect. Nevertheless, mass transfer limitation is encountered and Pd/C catalyst in the liquid bulk is not just useless but even catalyses product decomposition. In this study, the more selective Pd/Al₂O₃ catalyst was silanised with trichloromethyl silane to reduce its wettability and enrich the catalyst at the gas–liquid interface. The silanization did not affect the catalyst activity. In a stirred tank reactor, significantly higher hydrogen absorption rates were achieved for a flat interface but the effect decreased at higher stirring speed.