Abstract
In this work, we studied the effect of molybdenum precursors and the synthesis conditions on the final phase composition of bulk and supported molybdenum carbides and nitrides. Ammonium heptamolybdate, its mixture with hexamethylenetetramine, and their complex were used as the precursors at different temperatures. It was investigated that the synthesis of the target molybdenum nitrides strongly depended on the structure of the precursor and temperature conditions, while the synthesis of carbide samples always led to the target phase composition. Unlike the carbide samples, where the α-Mo2C phase was predominant, the mixture of β-Mo2N, MoO2 with a small amount of metal molybdenum was generally formed during the nitridation. All supported samples showed a very good dispersion of the carbide or nitride phases.
Highlights
There are three types of bonding between the transition metal and carbon or nitrogen atoms: metal bonding, covalent bonding, and ionic bonding [1]
This study set out the possibility of molybdenum carbide and nitride synthesis using various precursors and reaction conditions
It was investigated that the synthesis of target molybdenum nitrides strongly depends on the structure of the precursor and temperature conditions, while the synthesis of carbide samples always led to the target phase composition
Summary
There are three types of bonding between the transition metal and carbon or nitrogen atoms: metal bonding (metal-metal), covalent bonding (metal and non-metal), and ionic bonding (charge between metal and non-metal) [1]. The special crystal structure of transition metal carbides and nitrides is created by inserting carbon or nitrogen into the metal–metal bond is what makes its distance longer than the original. This special bond has exclusive electronic properties, which provide catalytic activity similar to the platinum group metals (Pt, Pd, Ru, etc.) in various reactions [2]. Molybdenum carbides are widely used as catalysts due to their activity in many reactions, in the water gas shift reaction, deoxygenation, denitrification, desulfurization, oxidation, partial oxidation, hydrotreating (HDS, HDO, HDN), dehydrogenation, isomerization, hydrogenolysis, hydrodemetallization, and methane reforming [4]. Possible difficulties in the application of these types of catalysts that may appear are most often related to obtaining those materials with high specific surface areas (usually less than 10 m2 /g) or high porosity
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