Nanosheet-Like Ho2O3 and Sr-Ho2O3 Catalysts for Oxidative Coupling of Methane

Abstract

In this work, Ho2O3 nanosheets were synthesized by a hydrothermal method. A series of Sr-modified Ho2O3 nanosheets (Sr-Ho2O3-NS) with a Sr/Ho molar ratio between 0.02 and 0.06 were prepared via an impregnation method. These catalysts were characterized by several techniques such as XRD, N2 adsorption, SEM, TEM, XPS, O2-TPD (temperature-programmed desorption), and CO2-TPD, and they were studied with respect to their performances in the oxidative coupling of methane (OCM). In contrast to Ho2O3 nanoparticles, Ho2O3 nanosheets display greater CH4 conversion and C2-C3 selectivity, which could be related to the preferentially exposed (222) facet on the surface of the latter catalyst. The incorporation of small amounts of Sr into Ho2O3 nanosheets leads to a higher ratio of (O− + O2−)/O2− as well as an enhanced amount of chemisorbed oxygen species and moderate basic sites, which in turn improves the OCM performance. The optimal catalytic behavior is achievable on the 0.04Sr-Ho2O3-NS catalyst with a Sr/Ho molar ratio of 0.04, which gives a 24.0% conversion of CH4 with 56.7% selectivity to C2-C3 at 650 °C. The C2-C3 yield is well correlated with the amount of moderate basic sites present on the catalysts.

Structural study of the rare earth compounds: Sm(OH)3, NdOHCO3, CeO2, and Ho2O3, prepared by Chemical Bath Deposition, and its correlation with crystal growth mechanism

“…No reflections other than are observed. The diffraction planes located at 2θ ~29.10°, ~44.00° and ~53.20° correspond to (222), ( 134) and (440) planes of Ho2O3 cubic phase, respectively [37]. Problems like polymorphic transitions, ions migration, slow crystallization and formation of crystalline aggregates stand out.…”

Surfactant-Assisted Preparation of Nanorod La2O3 Catalysts for Oxidative Coupling of Methane

“…The oxidative coupling of methane (OCM), as one of the direct CH 4 conversion routes to high value-added C 2 H 4 and C 2 H 6 , has attracted great attention since the early 1980s. , During the past 40 years, hundreds of catalysts including Li/MgO, , Mn/Na 2 WO 4 /SiO 2 , − rare earth metal oxides, − and perovskites − have been extensively investigated for the OCM reaction. Mn–Na 2 WO 4 /SiO 2 was recognized as the most promising catalyst for its outstanding C2+ selectivity. − Nevertheless, the high ignition temperature (T ≥ 750 °C) would result in high thermal stress on the catalyst and the loss or sintering of active components, , thus shortening the lifetime for its application in industry.…”