Impact of precursor sequence of addition for one-pot synthesis of Cr-MCM-41 catalyst nanoparticles to enhance ethane oxidative dehydrogenation with carbon dioxide

Dehydrogenation of Ethane to Ethylene by CO2 over Highly Dispersed Cr on Large-Pore Mesoporous Silica Catalysts

“…Increasing Cr loading above 4% leads to decreased Cr 6+ dispersion due to the formation of a non-active α-Cr 2 O 3 phase. These results are consistent with those obtained by Al-Awadi et al [16] and Asghari et al [17], who found that the bulk Cr 2 O 3 phase is dominant when Cr loading exceeds the monolayer coverage, which is 4% in our study. However, the samples with higher Cr concentrations (Cr(8)/LPMS-130 and Cr(11)/LPMS-130) possess a Cr surface density of more than 1 Cr atm/nm 2 Cr-atom•nm −2 (2.26 and 3.185 Cr atm/nm 2 , respectively), which clearly indicates that, after exceeding the monolayer coverage of LPMS-130, the concentration and size of non-redox α-Cr 2 O 3 phase are increased.…”

“…Increasing Cr loading above 4% leads to decreased Cr 6+ dispersion due to the formation of a non-active α-Cr2O3 phase. These results are consistent with those obtained by Al-Awadi et al [16] and Asghari et al [17], who found that the bulk Cr2O3 phase is dominant when Cr loading exceeds the monolayer coverage, which is 4% in our study. However, the samples with higher Cr concentrations (Cr 8 Figure 7A.…”

“…For these samples, the peaks at 577.6 and 586.63 eV characterize the Cr2p 3/2 and Cr2p 1/2 of the Cr 6+ ions, while the peaks at 575.68 and 585.17 eV are assigned to the Cr2p 3/2 and Cr2p 1/2 of Cr 3+ . Wang et al [7], Mimura et al [26], Weckhuysen et al [27], and Al-Awadi et al [16,28] have reported that the performance of chromium-based catalysts is intensely dependent on the Cr ions that dominate on the surface, whereas Cr species with a higher oxidation state show a higher performance during dehydrogenation reactions.…”

“…Based on the results in Table 3, it can be seen that all catalysts have a similar binding energy (BE) and the two oxidation states of chromium, Cr 3+ , and Cr 6+ coexisted on the surface of the catalysts, but with variations in their Cr 6+ /Cr 3+ ratios based on the Cr wt %. It is generally believed that reducible Cr species with a higher oxidation state (Cr 6+ ) is key to superior catalytic activity during the light alkane dehydrogenation reactions [13,16,17,[28][29][30][31]. Ge et al [30] used ESR and UV-DRS to explore the active site of the ODH reaction of C 2 H 6 with CO 2 over CrOx/silica catalysts, and found that species with high oxidation states are essential for this reaction.…”

“…Thus, the main challenge is maximizing CrO X species dispersion. However, more attention has been paid to mesoporous silicate materials, such as SBA-1 [14], SBA-15 [13], MSU-x [10,15], and MCM41 [16][17][18], which possess a larger surface area compared with commercial silica. Since the introduction of MCM41 mesoporous silica in 1992, the research in the mesoporous silicate nanomaterials area has been rapidly expanding and branching into separate categories that cover a wide range of sizes and structures of materials.…”