Crystal-phase-depended strong metal-support interactions enhancing hydrodeoxygenation of m-cresol on Ni/TiO2 catalysts

The relatively cheap and abundant Ni as a catalyst for hydrodeoxygenation (HDO) of biomass lignin-derived phenolics at 350 °C and atmospheric pressure suffers from unfavorable C-C hydrogenolysis toward CH4 with a lower direct deoxygenation (DDO) activity. Herein, we demonstrate that the activity and selectively of Ni for HDO of m-cresol can be modified through the differences of strong metal-support interaction (SMSI) on anatase and rutile TiO2. Characterizations showed that the presence of SMSI depended strongly on the crystal phase of TiO2. The SMSI dominates on Ni/a-TiO2 after reduction at 350 °C, resulting in Ni particles partially covered by a TiOx overlayer, and this overlayer became sufficiently thick at 650 °C, causing a significant reduction of CO chemisorption. Although the catalyst became selective for DDO to toluene, the overall HDO activity was significantly reduced because of excessive SMSI. In contrast, the Ni/r-TiO2 catalyst reduced at 350 °C exhibited little SMSI and was active for C-C hydrogenolysis like a bare Ni catalyst. Increasing reduction temperature to 650 °C, the Ni/r-TiO2 catalyst showed moderate SMSI and became selective to toluene through DDO while completely inhibited CH4 formation. The toluene and total aromatics yields were 84.8 and 92.2%, respectively, at full conversion. More importantly, the turnover frequency for DDO (2.43 min−1) on the Ni/r-TiO2 catalyst reduced at 650 °C was ∼40 and ∼14 times higher than that of Ni on rutile and anatase, respectively, reduced at 350 °C. This study provides an example of “Goldilocks principle” in catalysis, i.e., the best performing catalyst offers a balanced SMSI!