A novel approach to the synthesis of bulk and supported β-Mo₂C using dimethyl ether as a carbon source

Abstract

A novel approach to the synthesis of bulk and supported b-Mo 2 C using dimethyl ether as a carbon source † In view of the fact that H 2 was necessarily added into gas-state carbon sources in order to remove the surface carbon barrier for the complete carburization of Mo oxides to form Mo carbides, in this paper we proposed a simple synthetic route to overcome this issue. The current approach used a new carbon source, dimethyl ether (DME), as feed gas without H 2 addition and employed a pre-heating (PH) method before introducing DME into the reactor. With this novel approach we successfully prepared bulk and CNT supported molybdenum carbides. Note that the removal of carbon deposit by H 2 from DME thermal decomposition and PH-induced surface reconstruction can promote the carburization process. The formation mechanism of Mo carbides was proposed using X-ray diffraction (XRD) and rapid heating reaction mass spectrometry (RH-MS) characterizations. The complete synthesis process involved reduction-carburization of Mo precursors by DME and their thermal decomposition product CH 4 , via the pathway of MoO 3 / Mo 4 O 11 -MoO 2 -MoO x C y /MoC 1Àxb-Mo 2 C. The composition of gas-phase products was predominantly H 2 , CO and CH 4 with a very small amount of CO 2 and (or almost no) H 2 O.

Insights into the deactivation mechanism of metal carbide catalysts for dry reforming of methane via comparison of nickel-modified molybdenum and tungsten carbides

“…Because the fresh metal carbides were usually passivated before exposure to air, the surface region of all the samples should be dominated by metal oxide and (oxy)carbide layers. 30 As shown in Fig. 6, the fresh and used Ni-Mo 2 C (1/21) samples displayed four Mo species.…”

“…6, the fresh and used Ni-Mo 2 C (1/21) samples displayed four Mo species. The peaks at 228.4-228.7 eV Mo 3d 5/2 binding energy were assigned to the Mo 2+ in Mo 2 C, [30][31][32][33] and that at 229.2 eV, to the Mo d+ in oxycarbide. 30,34,35 The peaks at 230.3-230.6 and 232.0-232.2 eV binding energies were assigned to Mo 4+ and Mo 6+ species involved in Mo-O bonding, respectively.…”

“…The peaks at 228.4-228.7 eV Mo 3d 5/2 binding energy were assigned to the Mo 2+ in Mo 2 C, [30][31][32][33] and that at 229.2 eV, to the Mo d+ in oxycarbide. 30,34,35 The peaks at 230.3-230.6 and 232.0-232.2 eV binding energies were assigned to Mo 4+ and Mo 6+ species involved in Mo-O bonding, respectively. 34,36 In the case of fresh and used Ni-WC (1/21) samples, three oxidation states from surface W species were observed.…”

Molybdenum phosphide as a novel and stable catalyst for dry reforming of methane

“…5) revealed the formation of the Mo 2 C phase in the MoP-850 sample, more or less Mo 2+species in Mo 2 C should also exist on the MoP-850 surface. However, it was very difficult to distinguish between Mo σ+ in Mo 2 C (228.1-228.6 eV) 21,36 and Mo δ+ in MoP (228.0-228.4 eV) 32,37,38 by curve fitting because they were close to each other in terms of the Mo3d 5/2 binding energy. Note that the R1 (0.17) of used MoP-750 was just a little lower than that (0.21) of fresh MoP; however, the R1 (0.12) of used MoP-850 was much lower than that of fresh MoP.…”

First comparison of catalytic CO2 reduction to CO over molybdenum carbide, nitride and phosphide catalysts

“…2 and Table 2 that they all showed three Mo species: 228.4-228.8, 229.0-229.4 and 232.7-232.8 eV for Mo 2+ , Mo δ+ and Mo 6+ species, respectively. 35,36 Due to the fact that it was very difficult to distinguish among Mo-C (228.1-228.6 eV), 37,38 Mo-N (228.7-228.8 eV) 39 and Mo-P (228.0-228.4 eV) [40][41][42] by curve fitting, the Mo species in β-Mo 2 C, γ-Mo 2 N and MoP had to be uniformly assigned to Mo 2+ . In addition, there was a C 1s peak at 283.6 eV (known as the Mo carbide feature) 38 and a P 2p 3/2 peak at 129.7 eV (known as the Mo phosphide feature) 42 in the carbonized and phosphorized Mo/CNT samples, respectively, indicating the formation of Mo carbide during carbonization of Mo/CNTs and the formation of Mo phosphide during phosphorization of Mo/CNTs.…”