Methane activation over La2xY2-2xO3 (0 ⩽x ⩽ 1) catalysts

A+1Nb5+O3 (A = Li, Na, K) Perovskites with Different Fine Structures for Oxidative Coupling of Methane: Tracing the Crystalline Phase Effect on the Surface Active Sites

“…48 It was revealed that the C 2 product selectivity on ABO 3 perovskites and A 2 B 2 O 7 pyrochlores can be affected by the strength of the B−O bonds strongly, and a high C 2 yield corresponds generally to a weak B−O bond strength with a low binding energy. 19,20 To estimate the oxygen binding energy within the lattice matrix, we have thus calculated the average M−O bond energy (ABE), which can be given by eq 5 here: 48…”

“…19,20 The decreased strength of the B−O bonds can also influence the oxygen mobility of the catalysts, because the B−O bond is responsible for the generation of surface oxygen vacancies when enough energy is provided to break the bonds. 19,20 Compared to LiNbO 3 , NaNbO 3 and KNbO 3 possess close average Nb−O bond energy at room temperature, which is evidently lower than that of LiNbO 3 . FTIR results have validated that the Nb−O bond strength of the samples obeys the sequence of NaNbO 3 < KNbO 3 < LiNbO 3 .…”

“…The oxygen binding energy can provide an estimation of the energy barrier required to break a lattice metal–oxygen (M–O) bonds, and the unit cell free volume can mirror the oxygen anion mobility . It was revealed that the C 2 product selectivity on ABO 3 perovskites and A 2 B 2 O 7 pyrochlores can be affected by the strength of the B–O bonds strongly, and a high C 2 yield corresponds generally to a weak B–O bond strength with a low binding energy. , To estimate the oxygen binding energy within the lattice matrix, we have thus calculated the average M–O bond energy (ABE), which can be given by eq here: …”

“…On the other hand, by combining with different B-sites, the B− O bond strength could be tuned, which can influence the reducibility of the lattice O 2− and its surface vacancy concentration. 19,20 Through partially replacing the A-and Bsites with heterovalent cations of an ABO 3 perovskite, the surface basicity and O 2− vacancy concentration can be further tailored, which can extend to the surface and facilitate the generation of those active sites needed by the OCM reaction. 21,22 As previously reported, the OCM reaction performance on perovskites is influenced by surface A/B-site molar ratios, preparation methods, heterovalent cation doping, and modification with metal oxides and halides.…”

“…Over the past decades, quite a lot of catalysts have been studied, particularly including Mn/Na 2 WO 4 /SiO 2 , − Li/MgO, − rare earth oxides, − and perovskites. − Studies have substantiated that ABO 3 perovskites with an alkaline earth or rare earth metal A-site can often stand high temperatures and have potential applications for OCM. , Furthermore, the presence of A-site alkaline earth or rare earth metals can also provide surface basicity for ABO 3 compounds to stabilize the surface active oxygen anions such as O 2 – , O 2 2– , and O – , − which are important for an efficient OCM catalyst. On the other hand, by combining with different B-sites, the B–O bond strength could be tuned, which can influence the reducibility of the lattice O 2– and its surface vacancy concentration. , Through partially replacing the A- and B-sites with heterovalent cations of an ABO 3 perovskite, the surface basicity and O 2– vacancy concentration can be further tailored, which can extend to the surface and facilitate the generation of those active sites needed by the OCM reaction. , …”