Study on the reduction of commercial MoO₃ with carbon black to prepare MoO₂ and Mo₂C nanoparticles

Abstract

A simple method was developed to synthesize MoO 2 and Mo 2 C nanoparticles via controlling nucleation and growth in carbothermic reduction of commercial MoO 3 with carbon black. It was found that the appropriate C/MoO 3 molar ratio for preparation of Mo 2 C was 2.8, and the carbothermic reduction process followed the sequence: MoO 3 → transport phase (TP) → MoO 2 → Mo 2 C. It was revealed that the most crucial issues for controlling number of produced particles of product were migration of Mo source and aid of nucleating agent, which can be achieved by using MoO 3 and carbon black as starting materials. MoO 2 nanosheets with the thickness of 12 nm and lateral size of 60 nm, as well as Mo 2 C nanoparticles with particle size of 30 nm were prepared via reduction of MoO 3 with carbon black. However, MoO 2 and Mo 2 C produced via reducing MoO 3 by other kinds of carbon sources (activated carbon, graphite) or gas reductants (10% CH 4 /H 2 , CO) had much larger particle sizes of a few micrometers, which were tens of times than those using MoO 3 and carbon black, due to the too small amount of formed nuclei. The effects of C/MoO 3 molar ratio (0.5-2.8), molybdenum sources and carbon sources on the reaction mechanisms were investigated in detail. K E Y W O R D Scarbides, morphology, nanoparticles, nucleation, powders 918 | SUN et al.

β-Mo2C Nanoparticles Produced by Carburization of Molybdenum Oxides with Carbon Black under Microwave Irradiation for Electrocatalytic Hydrogen Evolution Reaction

“…In carburization processes with conventional heating, the carburization starts from the surface of the oxides to the interior, 29 with an initial reduction of MoO 3 to MoO 2 at temperatures of ∼500 °C. 30 We noticed that this behavior is consistent with our observations, where the experiments at low irradiation power (low temperature) show the reduction of MoO 3 to MoO 2 (Figure 2c) as the first step before carburization is achieved, similar to conventional processes. 30 Then, under a continuous microwave heating and higher power, the surrounding carbon atoms diffuse into the particle, replacing oxygen and eventually forming Mo 2 C. 24 The main difference is the intense, uniform, and rapid heating process achieved using microwaves.…”

“…30 We noticed that this behavior is consistent with our observations, where the experiments at low irradiation power (low temperature) show the reduction of MoO 3 to MoO 2 (Figure 2c) as the first step before carburization is achieved, similar to conventional processes. 30 Then, under a continuous microwave heating and higher power, the surrounding carbon atoms diffuse into the particle, replacing oxygen and eventually forming Mo 2 C. 24 The main difference is the intense, uniform, and rapid heating process achieved using microwaves. Here, the susceptor plays an important role because it is directly responsible for the microwave absorption and heat distribution.…”

“…EDX elemental analysis (Figure S2) identifies the presence and homogeneous distribution of Mo, C, and O, where the signal of O presumably originates from surface oxidation or absorbed oxygenated groups. In carburization processes with conventional heating, the carburization starts from the surface of the oxides to the interior, with an initial reduction of MoO 3 to MoO 2 at temperatures of ∼500 °C . We noticed that this behavior is consistent with our observations, where the experiments at low irradiation power (low temperature) show the reduction of MoO 3 to MoO 2 (Figure c) as the first step before carburization is achieved, similar to conventional processes .…”

Direct CVD Synthesis of MoS2 Monolayers on Glass by Carbothermal Reduction

“…CVD synthesis of the MoS 2 monolayer was performed using our thermodynamically stable synthesis method, , with solution-processed precursor preparation. Carbothermal reduction involves the reduction of molybdenum trioxide into MoO x or Mo and producing carbon oxides . Carbon black was chosen due to its small particle sizes that can aid better decomposition through close spacing with MoO 3 .…”

“…Carbothermal reduction involves the reduction of molybdenum trioxide into MoO x or Mo and producing carbon oxides. 28 Carbon black was chosen due to its small particle sizes that can aid better decomposition through close spacing with MoO 3 . To utilize carbothermal reduction in the CVD synthesis, solid MoO 3 powders were first dissolved in ammonium hydroxide (NH 4 OH) solution and carbon powders were then added to the solution (see the Methods Section for details and Figure 1a).…”