Ethane Dehydrogenation on Single and Dual Centers of Ga-modified γ-Al2O3

Density-functional theory calculations and microkinetic analysis are used to investigate the efficacy of Ga-modified gamma-Al2O3 (110) surfaces for the catalytic dehydrogenation of ethane and elucidate the synergy between Ga and Al sites. The model surfaces are modified by either Ga grafting or doping. We consider and analyze numerous active sites and rank them using microkinetic analysis. The kinetic parameters obtained from microkinetic modeling are compared with experimental values for ethane dehydrogenation over Ga2O3-Al2O3 mixed oxides prepared by coprecipitation. The dominant reaction pathway proceeds via heterolytic C-H bond dissociation to a surface proton and a metal-carbanion intermediate that undergoes beta-hydride elimination. We find that grafted Ga sites are catalytically inactive. In contrast, Ga-doped sites exhibit 5-fold enhancement in catalytic activity when compared to the sites on pristine Al2O3, owed to the synergy between neighboring Al-m and Ga-n, sites. Furthermore, we model and investigate the effect of surface hydroxylation, demonstrate how surface water interferes with the aforementioned synergy between Al-m and Ga-IV sites and discuss the implications for the catalytic activity of the modified surfaces. Increase in the partial pressure of H2O significantly increases the apparent activation energies of dehydrogenation and interestingly changes the most active site.

Automated summary

Density functional theory calculations and microkinetic analysis were used to investigate the efficacy of Ga-modified gamma-Al2O3 (110) surfaces for the catalytic dehydrogenation of ethane and the synergy between Ga and Al sites. It was found that doped Ga sites exhibited significantly higher catalytic activity compared to grafted Ga sites, and an increase in surface water interfered with the synergy between Al and Ga sites.