Effect of Mg substitution on LaTi_1−xMg_xO_3+δ catalysts for improving the C2 selectivity of the oxidative coupling of methane

Abstract

Mg substitution on B sites of La2Ti2O7 perovskites promoted changes in the surface active-site distribution leading to improvements in the C2 selectivity during the oxidative coupling of methane.

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

“…where v = IR wavenumber (cm −1 ), c = light speed (cm/s), μ = effective mass of B cations and oxygen, M B = atomic mass of B cations, and M O = atomic mass of oxygen (kg). 52 As shown in Table 4, the bond force constants follow the sequence of NaNbO It is evident that an A +1 Nb 5+ O 3 catalyst with a weaker Nb−O bond usually has better OCM performance. Therefore, by using different alkali metal A-sites to construct A +1 Nb 5+ O 3 perovskites, the Nb−O bond strength can be tailored, which could influence the OCM reaction performance of the final catalysts.…”

“…48 As shown in Table 4, the average metal−oxygen energy of A +1 Nb 5+ O 3 follows the sequence of KNbO 3 < NaNbO 3 < 4a, the peak around 600 cm −1 is ascribed to the Nb−O stretching vibrations, whose wavenumber follows the sequence of NaNbO 3 < KNbO 3 < LiNbO 3 . In FTIR spectroscopy, the bond force constant k can be used to measure the strength of a chemical bond, which are calculated by 52 v c…”

“…In contrast, both NaNbO 3 and KNbO 3 have much lower average M−O bond strength than LiNbO 3 , it is thus easier for the lattice distortion to happen at high temperatures. For these two samples, the lattice transformation from an orthorhombic or tetragonal 52,55,56 All the surface basic sites are beneficial to the activation of CH 4 molecules. 52,55,56 In particular, the moderate strength alkaline sites are accounting for the selectively generation of C 2 products, although they might not be active at low temperature because of CO 2 adsorption.…”

Oxidative Coupling of Methane: Perspective for High-Value C2 Chemicals

“…However, deactivation occurred in the Sr 0.1 LaO x -H catalyst during OCM in~30 h, but adding a small amount of Zr can produce better stability in OCM. Lopes et al [15] prepared La 2 Ti 2 O 7 -based catalysts (LaTi 1−x Mg x O 3+δ ) with varied Ti/Mg molar ratios through the partial substitution of Ti by Mg to regulate the quantities of alkaline sites and surface oxygen species, properties crucial for OCM reaction. The characterization data testifies that alkalinity and the surface oxygen vacancy concentration increase as Mg increases.…”

“…The non-oxidative processes involve the coupling of methane to olefins; this process suffers from intrinsic thermodynamic limitations and needs higher energy for large-scale applications [13]. Therefore, most of the research for direct conversion has emphasized a process called oxidative coupling of methane (OCM) [14][15][16][17][18][19].…”