This short review aims at providing an overview of the most recent literature regarding transition metal nitrides (TMN) applied in heterogeneous catalysis. These materials have received renewed attention in the last decade due to its potential to substitute noble metals mainly in biomass and energy transformations, the decomposition of ammonia being one of the most studied reactions. The reactions considered in this review are limited to thermal catalysis. However the potential of these materials spreads to other key applications as photo- and electrocatalysis in hydrogen and oxygen evolution reactions. Mono, binary and exceptionally ternary metal nitrides have been synthetized and evaluated as catalysts and, in some cases, promoters are added to the structure in an attempt to improve their catalytic performance. The objective of the latest research is finding new synthesis methods that allow to obtain smaller metal nanoparticles and increase the surface area to improve their activity, selectivity and stability under reaction conditions. After a brief introduction and description of the most employed synthetic methods, the review has been divided in the application of transition metal nitrides in the following reactions: hydrotreatment, oxidation and ammonia synthesis and decomposition.

Commercial carbon nanotubes (CNT), were used as supports to prepare Ni/CNT catalysts with a 15 wt% Ni loading and NiCu_x/CNT catalysts with Cu loadings of x: 1.5, 2.25, 3.0 and 3.75 wt% were prepared.

The effect of K promotion on the CO preferential oxidation (CO-PROX) reaction has been studied over Cu–CeO₂ based catalysts supported on carbon nanotubes (CNT) and reduced graphene oxide (G). The catalysts were prepared with 3 wt% Cu and 20 wt% CeO₂ loadings and 1 wt% K when promoted. In the CNT series, K loading was varied between 0.5 and 2 wt%. The catalytic performance and the characterization by powder X-ray diffraction (XRD), TEM-STEM, H₂-temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) have been presented. TEM analysis showed that the type of carbon support has an important effect on the dispersion of ceria, with the latter being higher for the CNT support. Addition of K to the catalysts improved the conversion of CO at lower temperatures. The characterization results reveal that the observed increases in the Cu⁺ species proportion and in lattice oxygen are related to the better catalytic performance.

Nickel-cobalt bimetallic catalysts supported on high surface area graphite with different Ni:Co ratios (3:1, 2:1 and 1:1) and the monometallic Ni and Co were prepared by wetness impregnation method. The catalysts were tested in hydrodeoxygenation (HDO) of guaiacol in the liquid phase at 50 bar of H₂ and 300 °C. The materials were characterized by N₂ adsorption–desorption, XRD, TEM/STEM, H₂-TPR, and CO-chemisorption to assess their properties and correlate them with the catalytic results. The activity was higher on the bimetallic catalysts and followed the trend NiCo_2:1/G ∼ NiCo_3:1/G > NiCo_1:1/G > Co/G > Ni/G. Also, selectivity results showed that Ni was more active in the hydrogenation favoring cyclohexanol production from phenol, while this was inhibited on the Co-containing catalysts. Hence, the results showed that synergy was created between Ni and Co and that their interaction, properties, and catalytic performance depend on the metals’ ratio.

Mitigation of anthropogenic CO₂ emissions possess a major global challenge for modern societies. Herein, catalytic solutions are meant to play a key role. Among the different catalysts for CO₂ conversion, Cu supported molybdenum carbide is receiving increasing attention. Hence, in the present communication, we show the activity, selectivity and stability of fresh-prepared β-Mo₂C catalysts and compare the results with those of Cu/Mo₂C, Cs/Mo₂C and Cu/Cs/Mo₂C in CO₂ hydrogenation reactions. The results show that all the catalysts were active, and the main reaction product was methanol. Copper, cesium and molybdenum interaction is observed, and cesium promoted the formation of metallic Mo on the fresh catalyst. The incorporation of copper is positive and improves the activity and selectivity to methanol. Additionally, the addition of cesium favored the formation of Mo⁰ phase, which for the catalysts Cs/Mo₂C seemed to be detrimental for the conversion and selectivity. Moreover, the catalysts promoted by copper and/or cesium underwent redox surface transformations during the reaction, these were more obvious for cesium doped catalysts, which diminished their catalytic performance.