Titania surface chemistry and its influence on supported metal catalysts

• Published in: Polyhedron 2019-09, Vol.170, p.41-50
• Main Authors: Mahdavi-Shakib, Akbar, Husremovic, Samra, Ki, Sohee, Glynn, Jessica, Babb, Lauren, Sempel, Janine, Stavrinoudis, Ioannis, Arce-Ramos, Juan-Manuel, Nelson, Ryan, Grabow, Lars C., Schwartz, Thomas J., Frederick, Brian G., Austin, Rachel Narehood
• Format: Article
• Language: English
• Subjects: Anatase; DRIFTS; Rutile; Surface chemistry; Titania
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2019.05.012

This work characterized the surface chemistry of a number of different titania samples. All commercial anatase samples were contaminated by sulfur. Hydrogen-bonded surface hydroxyls remained after calcination up to 400 °C for all anatase samples, in contrast to rutile and the pyrogenic titania materials P25 and P90, in which they were eliminated. Ru(0) catalysts on titania without hydrogen-bonded surface hydroxyls showed enhanced CO hydrogenolysis selectivity in the presence of water while Ru(0) catalysts on titania with hydrogen-bonded surface hydroxyls showed diminished selectivity in water, suggesting that surface hydrophilicity is important for this reaction. [Display omitted] This work characterized the surface chemistry of a number of different titania samples including four commercial anatase samples, an anatase sample that we synthesized, the pyrogenic titania samples P25 and P90, and a commercial rutile sample. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), were used to identified surface species that might interfere with the acid/base properties of the surface hydroxyls. All commercial anatase samples were contaminated by sulfur, which diminished their effectiveness as metal oxide supports for heterogeneous catalysis and has implications for their utility as photocatalysts. Hydrogen-bonded surface hydroxyls remained after calcination up to 400 °C for all anatase samples, in contrast to rutile and the pyrogenic titania materials P25 and P90, in which they were eliminated. Ru(0) catalysts on titania without hydrogen-bonded surface hydroxyls showed enhanced CO hydrogenolysis selectivity in the presence of water while Ru(0) catalysts on titania with hydrogen-bonded surface hydroxyls showed diminished selectivity in water, suggesting that surface hydrophilicity is important for this reaction. Heteroepitaxy between rutile RuO2 and rutile TiO2 is not essential for the creation of small evenly-spaced supported Ru(0) nanoparticles, which are important in many catalytic reactions.