On the Reactivity of Mo Species for Methane Partial Oxidation on Mo/HMCM-22 Catalysts

Abstract

By characterizing fresh and used Mo/HMCM-22 catalysts with ICP-AES, XRD, NH 3 -TPD technique, UV-Vis DRS and UV Raman spectroscopy, the reactivity of Mo species for methane partial oxidation into formaldehyde were directly studied with a new point of view. By comparing the fresh and used catalysts, it was found that the tetrahedral Mo species bonding chemically to the support surface were practically unchanged after the reaction, while the polymolybdate octahedral Mo species, which had a rather weak interaction with the MCM-22 zeolite, leached out during the reaction, especially when the Mo loading was high. Correspondingly, it was found from the time-on-stream reaction data that the HCHO yield remained unchanged, while CO x decreased with the reaction time during the reaction. By combining the characterization results and the reaction data, it can be drawn that the isolated tetrahedral molybdenum oxo-species (T d ) is responsible for HCHO formation, while the octahedral polyoxomolybdate species (O h ) will lead to the total oxidation of methane.

Studies on the SbOx species of SbOx/SiO2 catalysts for methane-selective oxidation to formaldehyde

“…In our previous work [22], SbOx/SiO 2 catalysts were prepared from SbCl 3 or SbCl 5 and investigated in methane-selective oxidation to formaldehyde. It was found that the formaldehyde yield obtained on SbOx/SiO 2 catalysts is close to recently reported results [23] for MoOx catalysts. However, little has been known about the speciation of the SbOx species in SbOx/ SiO 2 catalysts other than that the SbOx species can be easily spread on SiO 2 .…”

Microwave-assisted impregnation of highly dispersed Mo over HZSM-5 using various Mo precursors for methane dehydroaromatization

“…05-Reaction Chemistry & Engineering Paper 05058), which partly overlaps with the HZSM-5 intense peak observed at 27.5°. Nevertheless, the absence of a peak at 2θ = 27.3°in the case of Mo-impregnated catalysts points to the much higher degree of Mo dispersal in the zeolite interior or if they are present on the surface, possibly in the form of very small domains (>10 nm) to be detected by a diffractometer, 7,19,32,46 regardless of the impregnation procedure followed for the various Mo precursors. In addition, no peaks associated with the extra-framework molybdate quantities (Al 2 (MoO 4 ) 3 ) were detected in the XRD diffractogram of the as-synthesized catalysts, which may suggest that a small extent of dealumination of zeolitic framework occurs during the Mo incorporation process, 4 which was further corroborated with the 27 Al MAS NMR analysis discussed later.…”

Catalytic Performance of the Sb–V Mixed Oxide on Sb–V–O/SiO2 Catalysts in Methane Selective Oxidation to Formaldehyde

“…For Sb 5 [5,9]. It can be seen that the combinational use of antimony and vanadium components evidently enhances formaldehyde yield and the increment of formaldehyde yield, comparing with VO X / This formaldehyde yield obtained on Sb-V-O/SiO 2 catalysts is higher than recent results for single metal oxide catalysts such as molybdenum oxide [15] and vanadium oxide [5,9] catalysts.…”

“…Many supported single metal oxide or multi-component metal oxide catalysts have been widely studied in this reaction [4][5][6][7][8][9][10][11][12][13][14][15]. It was found that silica-supported vanadium and molybdenum oxide catalysts were more effective than other catalysts [8][9][10][11].…”

“…We know that, in the methane selective oxidation with O 2 as oxidant, vanadium oxide catalysts are more active than molybdenum oxide catalysts under same conditions and the formaldehyde yield obtained on vanadium oxide catalysts are generally higher than that for molybdenum oxide catalysts [12,13,15]. It is possible to achieve high methane conversion with remarkable formaldehyde selectivity by combinational use of antimony and vanadium oxides.…”