(544b) Group IB Metal Activated Anatase TiO2 for Selective Catalytic Deoxygenation of Lignin Fragments
- Conference: AIChE Annual Meeting
- Year: 2017
- Proceeding: 2017 AIChE Annual Meeting
- Group: Topical Conference: Innovations of Green Process Engineering for Sustainable Energy and Environment
Wednesday, November 1, 2017 - 12:55pm-1:20pm
As an abundant and representative component of lignin, guaiacol as a model compound has been widely studied in evaluating the effectiveness of hydrodeoxygenation catalysts. We recently discovered that Group IB metals such as Au and Ag, known for poor hydrogenation activity are capable of activating anatase TiO2 (TiO2-A) to generate unconventional hydrogenation sites for selective HDO of guaiacol by producing phenolics as the main products. While Au and Ag particles on several supporting materials, including rutile TiO2, ZrO2, Al2O3, SiO2, and activated carbon, did not show distinguishable performance compared to that of the supports alone in the conversion of guaiacol, these metals on anatase TiO2 support exhibited high activity with excellent stability and remarkable selectivity to phenolics in guaiacol hydrodeoxygenation. For example, at guaiacol conversion of 43% over a 0.4 wt% Au/TiO2-A-40 nm catalyst, the selectivity to phenolics reached 87%. No aromatics and saturated hydrocarbons such as cyclohexane were formed. Gold particle size ranging from 2.7 to 41 nm was found to affect the catalyst activity but not the product selectivity. The activity of the catalysts did not markedly decrease in accordance with the increase of Au particle size or the decrease of total surface area of the gold particles in the catalysts, suggesting that activated TiO2-A surface away from the interface between Au and the TiO2-A also contributed to the HDO performance.Â The reaction rates of 0.26 and 0.91 (minâ1 g-catâ1 cm3) were determined for guaiacol hydrogenation and catechol hydrogenation, respectively. Bimolecular methylation was established as the dominant mechanism for methyl group transfer from guaiacol to phenolics. While silver and copper showed similar selectivity at subnanometer particle sizes, considerably less Ag and Cu were effective to achieve similar guaiacol conversion levels as with Au/ TiO2-A. Temperature programmed reduction profiles of Ag/ TiO2-A and Cu/ TiO2-A showed that partial reduction of TiO2-A was enhanced by the presence of Ag and Cu. Only when TiO2-A reduction took place, the Group IB became active for the HDO, with phenolics as the only deoxygenation products.
Two major pathways of guaiacol hydrogenation to phenolics over anatase TiO2supported Group IB metals catalysts are proposed: (1) direct hydrogenation of guaiacol to form phenol and methanol, (2) hydrodehydroxylation of catechol intermediate formed from transmethylation between guaiacol and phenolics.
The pyrolytic product of a virgin lignin extracted from corn-stalk was studied with the catalysts. The results are consistent with the proposed mechanistic pathways in producing phenolic compounds.