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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.
Highlights
Propylene can be obtained from propane by non-oxidative or oxidative dehydrogenation pathways [1,2,3,4]
The samples of alumina annealed between 600 and 800 ◦C are characterized by relatively high specific surface areas, which vary in the Nanomaterials 2017, 7, 249 range of 250–270 m2·g−1, and narrow mesoporous-size distributions centered in the range of 4.4–5.0 nm (FiguNreanSom1a)t.erTialhs e20t1h7,e7r, m249al treatment at 900 ◦C brings about a significant reduction of specifi3cofs1u6rface area as well as broadening of the Barrett–Joyner–Halenda(BJH)pore size distribution
°C) a calcination temperature as high as 700 °C seems to be reasonable for the final thermal treatment ToafbAlel2O1.3-nP.hase composition and textural properties of SBA-15, CMK-3 and mesoporous supports obtained by nanocasting
Summary
Propylene can be obtained from propane by non-oxidative or oxidative dehydrogenation pathways [1,2,3,4]. The oxidative dehydrogenation of propane has not been commercialized yet, mainly due to problems with the control of selectivity with reasonable propane conversion (too much thermodynamically-favored COx is usually formed). Non-oxidative dehydrogenation of propane to propylene (PDH) is nowadays one of the most important forms of on-purpose technology for propylene production. Three type of PDH technologies—CATOFIN (Lummus Technology), Oleflex (UOP) and STAR (ThyssenKrupp Uhde)—have been developed on an industrial scale in more than 14 installations. Dozens of the new installations are already under construction or have been announced [3]
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