Effect of CO2 in the oxidative dehydrogenation reaction of propane over Cr/ZrO2 catalysts

Abstract

Investigation was made on the effect of chromium content, and method of hydrothermal preparation of Cr/ZrO 2 catalysts on their catalytic properties for CO 2 oxidative dehydrogenation of propane (ODP). The catalysts were characterized by nitrogen physisorption, X-ray diffraction, Raman spectroscopy, and temperature programmed reduction and desorption of CO 2 (TPD-CO 2). The Cr/ZrO 2 catalysts containing various chromium contents between 2.5 and 15 wt.% of Cr were prepared by conventional and microwave-assisted hydrothermal methods. Tetragonal ZrO 2 was formed, with higher Cr contents, and smaller crystallite sizes obtained using the microwave-assisted method. The relationship between selectivity to propene and propane conversion suggested that independent of the preparation method, the catalytic properties could be classified in two groups, with low and high chromium contents. The TPD-CO 2 results showed that a fraction of the CO 2 was desorbed at temperatures higher than 500°C, with simultaneous reduction of Cr(VI) species. The presence of CO 2 in the reactants caused strong decreases of activity, selectivity, and yield towards propene. These results suggested that CO 2 adsorbed strongly on the chromium oxide active sites for dehydrogenation of propane. The Cr/ZrO 2 catalysts were active and selective for dehydrogenation of propane in the absence of CO 2 (CDP), and became deactivated with time on stream. The activity was reestablished by thermal treatment with CO 2 or O 2 after deactivation in CDP catalytic cycles, with the activity always being reestablished by treatment in O 2. The deactivation occurred by reduction of Cr(VI) species and by deposition of carbonaceous species produced in oligomerization reactions.

Improved Catalytic Performance of Ethane Dehydrogenation in the Presence of CO2 over Zr-Promoted Cr/SiO2

“…The Raman spectra for the calcined catalysts are reported in Figure 6(l), the bands at 300, 350, 395, 550, 600, 850, and 987 cm –1 could be found for all the samples, they were assigned to the bending vibration mode of Cr–O–Cr, Cr 6+ species, the bending vibration mode of Cr 6+ –O in monochromate, Cr 3+ species, stretching mode of Cr–O–Cr, bridging mode of Cr–O–Cr, and symmetric stretching mode of Cr=O in poly-chromates, 39,40 respectively. The broad band centered at 987 cm –1 was probably related to the symmetric stretching mode of Cr=O in some kind of chromates with a lower polymerization degree because the Raman shifts of that in mono- and poly-chromates were 980 and 1010 cm –1 , 41,42 respectively. In addition, an isolated band at 890 cm –1 could be observed for the sample SrCr/SiO 2 , and it was overlapped for the rest.…”

One-Pot Synthesis of Ca Oxide-Promoted Cr Catalysts for the Dehydrogenation of Propane Using CO2

“…As we will illustrate, these catalysts contain different oxidation states of Cr and the levels of these different oxidation states also vary. The XRD could, in principle, identify the Cr 2 O 3 and Cr metal easily (high content and strong crystallinity) but not Cr­(VI) compounds as the latter is expected to be present in a non-crystalline form …”

Oxidative Dehydrogenation of Propane to Propylene in the Presence of CO2over Gallium Nitride Supported on NaZSM-5

“…Conventional routes for propylene synthesis involve naphtha steam cracking, refinery fluid catalytic cracking, etc. However, the propylene selectivity is always very low under high-temperature conditions. ,− Dehydrogenation of propane (DHP) represents a green and efficient way to produce propylene and has attracted much attention especially because the propane supply is abundant due to the development of shale gas technology. , …”