The Impact of V Doping on the Carbothermal Synthesis of Mesoporous Mo Carbides

Abstract

A series of bimetallic carbides of the form β-(Mo_1-xV_x)₂C (0 < x < 0.12) was synthesized by carbothermal reduction of corresponding h-Mo_1-xV_xO₃ precursors. The oxides were synthesized by precipitation, and the subsequent carbide phase development was monitored. The reduction mechanism is discussed on the basis of observed structural evolution and solid-state kinetic data. The reduction is observed to proceed via a complex mechanism involving the initial formation of defective Mo^IV oxide. Increasing the V content retards the onset of reduction and strongly influences the kinetics of carburization. The carbides exhibit a trend in the growth morphology with V concentration, from a particulate-agglomerate material to a packed, nanofibrous morphology. The high-aspect-ratio crystallites exhibit pseudomorphism, and in the case of the V-containing materials, some preferential crystal orientation of grains is observed. An increasing mesoporosity is associated with the fibrous morphology, as well as an exceptionally high surface area (80–110 m² /g). The synthesis was subsequently scaled up. By adapting the heating rate, gas flow, and pretreatment conditions, it was possible to produce carbide materials with comparable physical properties to those obtained from the small scale. As a result, it was possible to synthesize Mo₂C materials in multigram quantities (5–15 g) with BET surface areas ranging from 50 to 100 m² /g, among the highest values reported in the literature

Iron-Doped Molybdenum Carbide Catalyst with High Activity and Stability for the Hydrogen Evolution Reaction

“…62 Furthermore, Abudula et al claimed that a very small amount of Fe, Ni, or Co in β-Mo 2 C (~1.6%) displayed better activity and stability than pure β-Mo 2 C towards steam reforming of methanol. 63 Copromoted Mo carbides have been studied as a catalyst for hydrogenation of CO, 64,65 methane decomposition, 66,67 and hydrogen oxidation.…”

Carbon Dynamics on the Molybdenum Carbide Surface during Catalytic Propane Dehydrogenation

“…The as-prepared catalyst is free of these features, which confirms the optimized preparation process avoiding the formation of a coke overlayer by extended carburization. [15] At 500 8C, weak bands slowly arise, whereas the catalyst used at 550 8C is characterized by heavy coke deposition ( Figure 2). Similar observations are made on Pt-based catalysts.…”

“…We recently studied the formation mechanism of hcp b-Mo 2 C by carburization of hexagonal molybdenum oxide as well as the impact of its V doping (3 to 11%). [15] CNT-supported systems have also been investigated in methanol steam reforming [16] or higher alcohol synthesis. [17] The present work concerns the reactivity of Mo 2 C and V-doped Mo 2 C in propane activation including a detailed analysis of the active surface with the aim to improve our knowledge on the relations between phase composition, surface chemistry, and reactivity of molybdenum carbides in catalytic reactions of hydrocarbons.…”

The M1 Phase of MoVTeNbO as a Catalyst for Olefin Metathesis and Isomerization

“…The broad band of C 3 H 6 O ( m / z =58) centered at 470 K is consistent with the temporal formation of C 3 H 6 O detected upon increasing the reaction temperature in the catalytic test (Figure 1 b). A large consumption of propene with concurrent formation of oxygenated products was observed at approximately 750 K (which is much higher than the temperature range of the catalytic test) in the TPR profile (Figure 3); this is indicative of bulk reduction of the M1 catalyst by propene, which probably yields bulk metal carbide materials 22…”