Tungsten trioxide reduction-carburization with carbon monoxide-carbon dioxide mixtures: Kinetics and thermodynamics

Kinetics of nonisothermal reduction and carburization of WO3─NiO nano‐composite powders by CO─CO2

“…A similar observation has been made for completion of carburization by activated carbon . In reduction by CO of WO 3 , Nava Alonso et al . identified additional substoichiometric oxides of W 18 O 49 and W 20 O 58 whereas for reduction and carburization of W─Co oxides at 1080°C by Liu et al .…”

“…The apparent activation energy was calculated to be 35 kJ/mol for the reductions of NiO to Ni and WO 3 to WO 2 . In isothermal reduction of WO 3 by CO, the apparent activation energy for the conversion of WO 2 to W was 18 kJ/mol . The same reaction had an activation energy of 73 kJ/mol when it was performed isothermally under CH 4 /H 2 , and carburization of W had an activation energy of 96 kJ/mol .…”

Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture

“…According to thermodynamic data, [29,30] the decomposition of methane into carbon and hydrogen is possible above 823 K. Furthermore, Babutina et al, [31] reported that the formation of tungsten carbide with the reduction-carburization treatment of WO 3 in a methane atmosphere is thermodynamically possible at 773 K. However, methane decomposition can be described by the following reactions [10,32] : Methane begins to be adsorbed on the reduced surface where it dissociates into H ad and CH x or C atoms at the solid surface. Such an adsorption and decomposition is favored by the presence of Ni, which catalyses methane decomposition.…”

“…Some investigators [22,27] reported that not only hydrogen but also methane would take part in the reduction of tungsten oxide because CO and traces of CO 2 are formed in addition to H 2 O. Methane molecules may be adsorbed on the oxide surface and dissociate, which form active carbon species that have a large reducing capacity. [10] However, activation energies of reaction [1] for 0.5 and 0.46 Ni/(Ni + W) molar ratio mixtures are comparatively high. This observation may be because of a contribution of reaction [2] in the initial stages of the reduction.…”

“…In an early attempt, WO 3 was reduced and carburized in a single step with a CO-CO 2 mixture to form WC between 973 K and 1373 K. [10] The reduction of tungsten oxides was studied with use of CO. The intermediate products of this reaction were W 20 O 58 , W 18 O 49 , WO 2 , and WC 2 , with a final product of WC.…”