Effect of Hydrogen Spillover on the Ru/TiO₂-Catalyzed Guaiacol Hydrodeoxygenation: Rutile vs Anatase TiO₂

Abstract

The crystal phase of a catalyst support, such as TiO 2 , significantly contributes to the activity and stability of metalloaded catalysts by modifying the metal−support interactions. However, the effect of the crystal phase on hydrogen spilloverinduced hydrodeoxygenation (HDO) is relatively less understood, although the spillover of hydrogen on the reducible oxide support could play a crucial role in HDO by providing additional active sites. The HDO of guaiacol by hydrogen spillover was investigated by confirming the synergetic effect when pristine rutile and anatase TiO 2 were added to Ru-loaded TiO 2 , while hydrogen spilloverinduced promotion of guaiacol HDO performance was more pronounced for rutile TiO 2 than for anatase TiO 2 . Facilitated hydrogen spillover on rutile TiO 2 was confirmed by combined hydrogen temperature-programed reduction, hydrogen chemisorption, and hydrogen diffuse reflectance infrared Fourier transform analysis. The distinctive adsorption behaviors of the reactants on rutile and anatase TiO 2 were evaluated by using attenuated total reflectance infrared spectroscopy, which demonstrated that the adsorption behavior was also responsible for the spillover-induced promotion of the HDO performance. This study facilitates the understanding of the distinctive features of spillover hydrogen affecting HDO according to the phase of TiO 2 , which can provide guidelines for designing catalysts with enhanced HDO performance.

Hydrodeoxygenation of guaiacol over physically mixed Co/TiO2 and WO3/TiO2 catalysts

“…Therefore, for the Ru-loaded TiO 2 (R) catalyst, the reduction was performed at 300 °C, as reported in previous studies from our group. 10,21,34,36 The transition-metal-loaded catalysts were activated by reduction at 500 °C.…”

“…Because 2-methoxycyclohexanol ( 6 ) could be further converted into cyclohexanol ( 4 ) over a prolonged reaction time, 34 it should be noted that the higher cyclohexanol ( 4 ) yield obtained with the Co catalyst (which was obtained at 100% guaiacol conversion) might be attributed to the greater progress of the reaction on the Co catalyst compared to that on the Ru catalyst. To determine whether the difference in the product distribution obtained with the Co and Ru catalyst (the absence of 2-methoxycyclohexanol ( 6 ) in the product obtained with the Co catalyst) resulted from the difference in the extent of progress of the reaction, or whether the two catalysts led to distinct reaction pathways, guaiacol HDO was performed at a lower conversion to determine the distribution of the reaction intermediates over each catalyst.…”

“…13–17 To investigate the effect of introducing the tungsten oxide promoter, catalysts with cobalt impregnated solely on the TiO 2 support (Co(10)/TiO 2 (R) and Co(10)/TiO 2 (A)) and catalysts co-impregnated with cobalt and tungsten oxide (Co(10)WO x (10)/TiO 2 (R) and Co(10)WO x (10)/TiO 2 (A)) were synthesized. Because the phase of the TiO 2 support (rutile or anatase) could significantly modulate the dispersion of the supported active metal and the activity of the TiO 2 supported catalysts, 34,39 both rutile TiO 2 and anatase TiO 2 were tested as supports to examine the effect of the TiO 2 phase on the catalytic activity. Prior to evaluating the activity of the synthesized catalysts for guaiacol, a series of catalyst characterizations was performed.…”

“…The atomic content of the catalysts was obtained from inductively coupled plasma atomic emission spectroscopy (ICP-AES) using an ICP-OES spectrometer (OPTIMA 8300, PerkinElmer). X-ray photoelectron spectroscopy (XPS) analysis was performed using the same methods as in our previous studies, 10,34 and the deconvolution of W 4f peaks was conducted using the parameters described in the reference. 35…”

“…Although anatase TiO 2 has been more widely investigated as a catalyst support, our previous study revealed that Ru loaded rutile TiO 2 showed higher HDO performance compared to the Ru loaded anatase TiO 2 catalyst, which was attributed to higher dispersion and facilitated hydrogen spillover. 34 Among the various transition-metal-loaded catalysts, Co-loaded TiO 2 showed superior activity in the HDO of guaiacol to yield cyclohexanol, and the removal of the methoxy group of guaiacol was achieved more economically using the Co-loaded catalyst than by using the Ru-loaded catalyst. To accomplish complete removal of oxygen functional groups, the tungsten oxide-loaded TiO 2 catalysts were physically mixed with Co catalysts.…”