Akademik Veri Yönetim Sistemi
JOURNAL OF THE FACULTY OF ENGINEERING AND ARCHITECTURE OF GAZI UNIVERSITY, cilt.36, sa.2, ss.1075-1088, 2021 (SCI-Expanded)
Cr-based catalysts are widely used in dehydrogenation reactions. In this study, it was aimed to investigate the effects of Cr content on catalyst structure, chromate type and amount. First, the catalyst support MCM-41 was synthesized hydrothermally, and then xCr@MCM-41 (x: 4,6,8,10) catalysts in different mass % ratios were prepared by the impregnation technique. The active monochromates for the reaction was obtained on 4Cr@MCM41 catalyst at the highest amount. It was shown that Cr metal homogeneously distributed in this catalyst structure. Catalytic tests (600., atmospheric) were carried out on the 4Cr@ MCM-41 catalyst selected for its proper crystal size, homogeneous metal distribution and high amount of active monochromate content. As a result of the catalytic tests, high isobutane conversions (80%) were obtained up to the 60th minute and high isobutene selectivity (95%) after the 40th minute. The observed high conversions were explained by the transformation of Cr(II)O-2(-2), formed by tetrahedrally coordinated Cr(VI)O4-2 structures in the catalyst, into active Cr(III)O-3(-3) species by using the water in the support structure. After the reaction, it was shown that only <0.1% carbon deposition was detected in the catalyst and the catalyst deactivation was caused by the Cr form change. It was determined that the crystallite size increased (40%) after the reaction, depending on the conversion of Cr+6 to Cr+3. It was also shown that this form change enabled the catalyst surface acidity to be reduced, especially Lewis acid sites, thus increasing isobutene selectivity and preventing coke formation. For xCr@MCM-41 catalysts synthesized by impregnation technique, a 4%Cr content by mass appears to be an appropriate ratio for high isobutene selectivity and high amount of monochromate formation.