Abstract
<p>Titania supported chromia catalysts have been employed for selective catalytic reduction (SCR) process because of their higher activity and selectivity. The catalytic activity of the titania supported chromia system is owing to the stabilization of the anchored chromia species having multiple chemical and molecular states on the surface<strong>. </strong>In the present work an attempt has been made to prepare titania supported chromia catalysts, from TiCl<sub>4</sub> and CrO<sub>3</sub> as precursors for the support and active phase respectively. Characterization of the catalysts have been made using FTIR spectroscopy and thermo analytical techniques such as thermogravimetric analysis (TGA), evolved gas analysis (EGA) and temperature programmed reduction (TPR). The EGA, TGA and FTIR results indicate that the surface hydroxyl groups of TiO<sub>2</sub> (gel) has an influence on the chemical state of the chromium. Due to the surface anchoring, Cr<sup>+5</sup> species have been detected on the surface of the fresh catalyst which decomposes to lower valence state on calcination. EGA results indicate that Cr<sup>+3</sup> species having higher degree of coordinatively unsaturated centers is stabilized by gel titania as support. EG analysis and FTIR studies illustrate the coverage of the surface with similar type of sites at 10 wt.% chromia loading. TPR studies demonstrate the presence different kinds of surface chromia species with respect to chromia content.</p>
Highlights
Supported chromia catalysts are widely used in industrial catalysis for dehydrogenation, polymerization and oxidation reactions owing to their ability of various supports to stabilize different chemical states on the surface [1]
The intensity of the band at 1631 cm-1 and 3400 - 3600 cm-1 decreases with increase in chromia content
The diffused peak at 3400 - 3600 cm-1 is due to the surface hydroxyl and at higher chromium content (10%) due to anchoring of the chromia species through the surface hydroxyl one finds a decrease in its intensity
Summary
Supported chromia catalysts are widely used in industrial catalysis for dehydrogenation, polymerization and oxidation reactions owing to their ability of various supports to stabilize different chemical states on the surface [1]. The catalytic activity for dehydrogenation of isobutene over CrOx/TiO2 has been found to be relatively more active per unit surface area of the catalyst [5,6]. The knowledge of the surface characteristics of the supported chromia system is essential in order to comprehend the dynamics of their catalytic behaviour towards various industrially significant catalytic reactions. In the present study we have made an effort to characterise the surface properties of the laboratory synthesized titania (TiO2 gel) supported chromia catalysts as a function of calcination temperature and chromia. 2002 al-Farabi Kazakh National University loading using spectroscopic and thermoanalytical techniques
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