Editorial: Transition Metal Catalysts—Design, Synthesis, and Applications

Transition metals occupy a unique and pivotal position at the intersection of chemistry, materials science, and biology, owing to their diverse electronic configurations, variable oxidation states, and rich coordination chemistry. These intrinsic properties empower transition metals with exceptional versatility, serving as key functional components in a wide range of fields, including homogeneous and heterogeneous catalysis [1,2,3,4,5,6,7,8,9,10,11,12,13,14], structural alloys [15,16,17,18,19,20,21,22,23], electronic devices [24,25,26,27,28,29,30,31,32], and biological systems [33,34]. In the field of catalysis, transition metals can promote various chemical transformations with outstanding efficiency and selectivity, smoothing numerous industrial processes and accelerating the synthesis of high-value-added chemicals [23,35,36,37,38,39,40,41,42]. Furthermore, the incorporation of transition metals into structural materials has also driven the development of advanced alloys and composite materials, which exhibit superior mechanical strength, corrosion resistance, and thermal stability.

Recent advances in synthetic methodologies and characterization techniques have significantly expanded the functional potential of transition metal-based systems. Through the rational design of coordination complexes, nanostructured materials, and single-atom catalysts, researchers achieved further precision in reaction activity controlling. There is now growing interest in utilizing earth-abundant metals as sustainable alternatives to precious metals, alongside efforts to develop finely tunable ligands to achieve precise control over catalytic cycles. Transition metals also play a central role in next-generation electronic and optoelectronic technologies, encompassing conductive polymers, spintronic materials, and energy storage devices such as batteries and supercapacitors [43,44,45,46,47,48]. Furthermore, transition metal complexes are attracting increasing attention as therapeutic drugs, diagnostic probes, and imaging agents with the prominent ability to selectively interact with biomolecular targets [49,50,51,52,53,54,55,56,57,58,59,60].

Despite these advances, there are still limitations existing that hinder the widespread implementation of transition metal-based applications. Catalyst deactivation, insufficient understanding of the mechanisms of catalytic processes at the molecular level, limited selectivity under complex reaction conditions, difficulties in scaling up synthetic processes, and concerns regarding toxicity and environmental effect remain major obstacles that urgently need to be well addressed.

The Special Issue “Transition Metal Catalysts: Design, Synthesis and Applications” of Inorganics brings together eight research papers, showcasing the latest advancements in transition metal-based systems across catalyst development, mechanistic exploration, and practical applications, highlighting the diversity and versatility of transition metal catalysts in modern research.

One of the key themes explored in this Special Issue is the rational control of catalyst composition and structure to enhance catalytic performance. In this context, the study from Prof. Puello-Polo and co-workers investigated the effect of potassium oxide doping on the performance of a ternary CoMo–Ni/Al₂O₃ catalyst in the hydrogenation–deoxygenation (HDO) reaction of guaiacol [61]. K₂O doping significantly enhances the selectivity for prepared catalysts in the HDO reaction without compromising catalytic activity, and the selectivity increased progressively with K₂O loading where the catalyst containing 5 wt% K₂O reached 65% HDO and 81.3% selectivity toward cyclohexane. Kinetic analysis further reveals that potassium promotes demethylation and demethoxylation pathways while suppressing competing rearrangement reactions, thereby providing valuable theoretical guidance for catalyst design strategies in biomass upgrading and conversion.

The work from Prof. Xue’s group further underscores the importance of catalyst preparation methodologies—the “support reducibility regulation” strategy aimed at constructing strong basic sites on the surface of solid catalysts under mild reaction conditions [62]. By introducing Cr³⁺ into the mesoporous zirconia framework, the authors successfully constructed a support with reducibility, which can induce the decomposition of KNO₃ at low temperatures via redox pathways generating highly dispersed, strongly basic K₂O species. Compared with traditional calcination-based thermal decomposition methods, this strategy reduces the activation temperature by about 300 °C for the formation of basic sites while effectively preserving the integrity of the mesoporous support structure. The resulting catalyst exhibits outstanding catalytic performance in the transesterification reaction for the synthesis of dimethyl carbonate, outperforming classic solid base catalysts such as MgO. This work fully demonstrates how rational control of support properties can lead to efficient, energy-saving catalyst preparation methods.

Another important aspect of catalyst design lies in the intrinsic relationship between synthetic conditions and catalyst morphology. In the study reported by Prof. Friedrich, the authors prepared VOx/MgO catalysts with a solution-combustion synthesis method using varying molar ratios of glycine to oxidant during the synthesis process, studying the effects on morphology, phase composition, surface area, crystallite size, elemental distribution, and coordination environment around V [63]. The combustion temperature, determined by the fuel content, significantly influences the catalyst’s morphology, specific surface area, and grain size. Notably, the catalyst prepared under stoichiometric combustion conditions exhibited excellent catalytic performance in the oxidation dehydrogenation (ODH) reaction of n-octane. Structural analysis revealed that the sample uniquely contains a magnesium vanadate phase which plays a key role in catalytic activity. This work highlights how carefully adjusting synthesis parameters by controlling phase formation and nanostructure can lead to enhanced catalytic performance.

In addition to experimental catalyst development, theoretical studies are crucial for understanding catalytic mechanisms at the molecular level. The work from Prof. Hong and Prof. Zhang utilized density functional theory (DFT) calculations to investigate the mechanism of Ru(II)-catalyzed amination of aminopyridines via η⁶-coordination activation [64]. The computational analysis indicates that both ortho and para substitution patterns follow a similar stepwise mechanism involving a Meisenheimer intermediate. Due to the weaker orbital interactions between the CpRu(II) fragment and the para-substituted Meisenheimer intermediate, the para pathway suffers from a significantly higher energy barrier.

Transition metal catalysts also play a significant role in addressing challenges in the environmental and biomedical fields. In Prof. Torres-Palma’s work, the authors investigated transition metal-doped graphitic carbon nitride (g-C₃N₄) photocatalysts for antimicrobial applications [65]. By adjusting the synthesis temperature and introducing transition metals such as Mn, Co, and Cu, the researchers achieved enhanced photocatalytic disinfection performance through improved charge separation efficiency and reactive oxygen species (ROS) generation capacity. The optimized Mn-doped g-C₃N₄ material achieved complete inactivation of E. coli within 6 h; the prepared graphitic carbon nitride was also integrated into a sodium alginate hydrogel surface, affording a reusable, self-cleaning antimicrobial surface.

Prof. Barajas-Solano and co-workers further explore environmental remediation issues, utilizing magnetite-catalyzed ozonation, anaerobic digestion, and microalgal cultivation to treat leachate from sanitary landfills [66]. The study demonstrates that catalytic ozonation significantly enhances the biodegradability of the leachate, enabling coupling with upflow anaerobic sludge blanket (UASB) reactor to reach optimal methanogenic activity. The subsequent microalgal treatment stage further enhanced the removal of nutrients, particularly nitrogen and phosphorus. Although further optimization is needed to fully meet discharge standards, this work demonstrates the application potential of integrating catalytic and biological processes for treating complex wastewater systems.

The design of catalytic support is another key factor influencing catalyst performance. In the work of Prof. Rinaudo, the researchers employed a cerium oxide support doped with Zr, Pr, and Tb to prepare Pt catalyst for the selective oxidation of glycerol with excellent activity [67]. Detailed characterization results revealed that the nature of doping elements alters the properties of the support by increasing the concentration of oxygen vacancies as well as electron mobility, thereby modifying the oxidation state and dispersion of the platinum nanoparticles. In the systems studied, the Pt/CeTb catalyst exhibited the highest turnover frequency (TOF) and enhanced selectivity toward glycerol acid. This superior performance was attributed to the synergistic effects of oxygen vacancies, strong metal–support interactions, and optimal metal particle size.

Finally, Prof. Sosa-Torres and co-workers delve into the mechanistic complexity of transition-metal-mediated oxidation reactions combined with DFT calculations to provide an in-depth investigation of the oxidative dehydrogenation of pyridinium iron complexes [68]. This work reveals that nitrogen-centered radical intermediates play a key role in the reaction pathway, and molecular oxygen acts as a hydrogen acceptor via a hydrogen atom transfer mechanism, rather than forming high-valent iron–oxygen species. The high agreement between experimental measurements and computational results provides strong evidence for the proposed reaction mechanism and offers new insights into iron-mediated oxidative transformations, particularly those involving biomimetic catalysis.

Overall, the research included in this Special Issue fully demonstrates the breadth of the modern field of transition metal catalysis, covering multiple aspects such as catalyst design, mechanistic investigations, and practical applications. These research findings further demonstrate the vital role of rational control of catalyst composition, including the selection of dopants, co-catalysts, and support materials, in catalyst performance, and transition metal catalysts continue to offer highly promising solutions to various pressing societal challenges, including the production of sustainable chemicals, the remediation of environmental pollution, and the development of antimicrobial technologies. The findings and achievements here vividly depict the dynamic and rapidly evolving landscape of transition metal catalysis, and we sincerely hope that the research results presented in this Special Issue will inspire further research enthusiasm and collaboration, thereby driving the continuous development and refinement of efficient, sustainable catalytic systems based on transition metals.