Adsorption and catalytic thermolysis of gaseous urea on anatase TiO2 studied by HPLC analysis, DRIFT spectroscopy and DFT calculations

High-purity gaseous urea was generated by passing a carrier gas at 100 °C through an inert cordierite monolith impregnated with urea, and the gaseous urea adsorbed onto anatase TiO2 catalyst samples. Urea adsorption on the catalysts was confirmed by two independent methods: high performance liquid chromatography (HPLC) analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Moreover, urea adsorption at the anatase (1 0 1) surface was studied by density functional theory (DFT) calculations. In combination with the DRIFT spectra, the DFT calculations indicated that two different adsorbed states of deprotonated urea were present on the catalyst simultaneously: in one adsorbed state, urea bound at one Ti site, and in the other adsorbed state urea was rotated and bound at two Ti sites. The confirmation of urea adsorption on anatase supports our previous finding that urea thermolysis is a catalytic reaction.

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► High-purity gaseous urea was adsorbed onto anatase TiO2 at 100 °C.
► Urea adsorption was confirmed by HPLC analysis and by DRIFT spectroscopy.
► DFT calculations indicated two different adsorbed states of urea.