The critical role of the surface WO4 tetrahedron on the performance of Na-W-Mn/SiO2 catalysts for the oxidative coupling of methane

Transient Potassium Peroxide Species in Highly Selective Oxidative Coupling of Methane over an Unmolten K2WO4/SiO2 Catalyst Revealed by In Situ Characterization

“…The O 1s, K 2p, and W 4f photoemission features of the catalyst at elevated temperatures under an O 2 atmosphere (13 Pa) are shown in Figure a, while the detailed fitted peak information is summarized in Table S1. First, at 410 °C, the O 1s peaks were located at 530.3, 531.0, and 532.4 eV, which are consistent with the reported O 1s peak positions of TiO 2 , K 2 WO 4 , and SiO 2 , respectively. ,, Two new peaks (536.4 and 538.0 eV) appeared when the temperature was elevated to 560 and 680 °C. These newly appeared peaks were assigned to O 1s of peroxide (K 2 O 2 ) and superoxide (KO 2 ) species, respectively, which were formed according to Reactions and .…”

“…First, at 410 °C, the O 1s peaks were located at 530.3, 531.0, and 532.4 eV, which are consistent with the reported O 1s peak positions of TiO 2 , K 2 WO 4 , and SiO 2 , respectively. 29,33,34 Two new peaks (536.4 and 538.0 eV) appeared when the temperature was elevated to 560 and 680 °C. These newly appeared peaks were assigned to O 1s of peroxide (K 2 O 2 ) and superoxide (KO 2 ) species, respectively, which were formed according to Reactions 13 and 15.…”

“…Under the same atmosphere (13 Pa O 2 ), at 410 °C, the peaks of K 2p were located at 293.4 eV (2p 3/2 ) and 296.2 eV (2p 1/2 ), which were consistent with the reported values of K 2 WO 4 . 29,33 After the sample temperature was increased to ≥560 °C, photoemission peaks from K 2p became broader, and two new peaks (294.4 and 297.2 eV) appeared with binding energies 1.0 eV higher than those at 410 °C. These new peaks with higher binding energy suggested a definite change in the chemical environment of the K cations after being heated from 410 to 560 and 680 °C in an O 2 atmosphere.…”

Progress in studies of natural gas conversion in China

“…Liu et al (1998) found that addition of 3 vol% of CO 2 into methane could slow down the carbon deposition of the catalyst, and improve the stability of the catalyst. Accordingly, Li et al (2004) proposed combining exothermic reaction of oxidative coupling of methane (OCM) with endothermic reaction of MDA. By such a way, the byproduct CO 2 of OCM reaction can be used to improve the stability of catalyst Mo/HZSM-5 for MDA reaction.…”

“…A novel route for syngas production using lattice oxygen of composite oxide instead of molecular oxygen was developed (Li et al, 2004). In this route, the composite oxide acts as an oxygen carrier and syngas is produced by using a reduction-oxidation cycle.…”