Catalytic Behavior of Chromium Oxide Supported on Nanocasting-Prepared Mesoporous Alumina in Dehydrogenation of Propane

Abstract

Mesoporous alumina with narrow pore size distribution centered in the range of 4.4–5.0 nm and with a specific surface area as high as 270 m2·g−1 was prepared via the nanocasting approach using a CMK-3 carbon replica as a hard template. Based on this support, a series of catalysts containing 1, 5, 10, 20 and 30 wt % of chromium was prepared by incipient wetness impregnation, characterized, and studied in the dehydrogenation of propane to propene (PDH). Cr species in three oxidation states—Cr(III), Cr(V) and Cr(VI)—were found on the oxidized surface of the catalysts. The concentration of these species varied with the total Cr loading. Temperature-programmed reduction (H2-TPR) and UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS) studies revealed that Cr(VI) species dominated at the lowest Cr content. An increase in the Cr loading resulted in an appearance of an increasing amount of Cr(III) oxide. UV-Vis-DRS measurements performed in situ during the PDH process showed that at the beginning of the catalytic test Cr(VI) species were reduced to Cr(III) redox species. A crucial role of the redox species in the PDH process over the catalysts with the low Cr content was confirmed. The stability test for the catalyst containing 20 wt % of Cr showed that this sample exhibited the reproducible catalytic performance after the first four regeneration–dehydrogenation cycles. Moreover, this catalyst had higher resistance on deactivation during the PDH process as compared to the reference catalyst with the same Cr loading, but was supported on commercially available alumina.

State-of-the-art catalysts for direct dehydrogenation of propane to propylene

“…Supported CrOx are one of the most efficient catalysts for alkane dehydrogenation that have been studied for several decades [17,[28][29][30][31][32][33][34][35][36][37]. Owing to the low price and high catalytic activity, CrOx-based catalysts have been commercially utilized in Catofin craft [21,23,24].…”

“…On fresh CrOx-based catalysts, there are many kinds of Cr species, including Cr 6+ , Cr 5+ , Cr 3+ , Cr 2+ , isolated Cr n+ , oligomeric Cr n+ , and crystallite Cr2O3, which play different roles in the PDH process [30][31][32]. Rather difficultly, the Cr 6+ species would be transformed into Cr 3+ and/or Cr 2+ during the PDH process due to the presence of H2 [30,32].…”

“…On fresh CrOx-based catalysts, there are many kinds of Cr species, including Cr 6+ , Cr 5+ , Cr 3+ , Cr 2+ , isolated Cr n+ , oligomeric Cr n+ , and crystallite Cr2O3, which play different roles in the PDH process [30][31][32]. Rather difficultly, the Cr 6+ species would be transformed into Cr 3+ and/or Cr 2+ during the PDH process due to the presence of H2 [30,32]. Furthermore, the types of supports, Cr loading amounts, and preparation methods can have great influences on the types of Cr species present, and thereby, affect the catalytic performances of CrOx-based catalysts [31,[33][34][35].…”

“…A series of metal oxides (such as Al2O3, SiO2, and ZrO2) have been studied as supports of CrOx catalysts [18,24,[28][29][30][31][32][33][34][35][36][37][38][39]. In these CrOx-based catalysts, the supports play an important role in determining the dispersion (such as isolated Cr n+ , oligomeric Cr n+ , and crystallite CrOx species), states (such as Cr 6+ , Cr 5+ , Cr 3+ , and Cr 2+ ), structure, and electronic properties of the Cr species, thus affecting their catalytic activity, stability, and anti-coking capability in the PDH process.…”

Recent Progress in Commercial and Novel Catalysts for Catalytic Dehydrogenation of Light Alkanes

“…synthesized a mesoporous Cr 2 O 3 /Al 2 O 3 catalyst using MIL‐101, achieving a strong interaction between Cr species and alumina support, resulting in a high selectivity to isobutene and a good stability. Moreover, the nanocasting approach using a CMK‐3 carbon replica as a hard template has been attempted to prepare mesoporous alumina. CrO x on mesoporous alumina showed both higher resistance to deactivation and enhanced stability.…”