Guaiacol hydrotreatment in an integrated APR-HDO process: Exploring the promoting effect of platinum on Ni–Pt catalysts and assessing methanol and glycerol as hydrogen sources

This study presents an integrated approach combining aqueous phase reforming (APR) and hydrodeoxygenation (HDO) for the hydrotreatment of guaiacol, a model compound representing lignin-derived phenols in pyrolysis bio-oils. The APR process enables in-situ H2 generation, eliminating the need for an external hydrogen source. We examine the interplay between metal species, the Pt-promoting effect on Ni–Pt catalyst supported on activated carbon (AC), and the choice of hydrogen source (methanol or glycerol). Amongst the monometallic catalysts, a 1% Pt/AC catalyst notably achieved over 96% guaiacol conversion at 300 °C with either hydrogen source. Interestingly, when 0.5–1% of the Ni loading is replaced with Pt, the resulting bimetallic Ni–Pt/AC catalysts demonstrate a significant improvement in guaiacol conversion, reaching 70% when methanol is employed as the hydrogen source. Surprisingly, no comparable enhancement in guaiacol conversion is observed when employing glycerol as the hydrogen source. This observation underlines one of the pivotal effects of the hydrogen source on catalyst performance. X-ray photoemission spectroscopy (XPS) pinpointed strong Ni–Pt interactions in the catalyst. It also revealed distinctive electronic features of Ni–Pt/AC, which are favourable for steering selectivity towards cyclohexanol rather than phenol when Pt loading is increased from 0.5 to 1%. Moreover, Pt enhanced catalyst stability by inhibiting the oxidation of Ni sites and mitigating Ni–Pt phase sintering. Overall, our findings offer important insights into integrating APR and HDO processes, the promotion effect of Pt, and the importance of hydrogen source selection in terms of guaiacol conversion and catalyst stability. Financial support for this work was provided by the Department of Chemical and Process Engineering at the University of Surrey and the EPSRC grant EP/R512904/1 as well as the Royal Society Research Grant RSGR1180353. Authors would also like to acknowledge Spanish Ministry of Science and Innovation through the projects MAT2016-80285-P, RYC2018-024387-I, JC2019-040560-I. RR acknowledges the financial support provided by the ERC Consolidator Grant (LIGNINFIRST, project number 725762). This work was also partially funded by the University of Seville via the VI PPIT grant scheme for talented researchers and the Junta de Andalucia PAIDI2020 programme through the CLEVER-BIO project P20_00667.