Disclosing the Role of Gold on Palladium – Gold Alloyed Supported Catalysts in Formic Acid Decomposition

Phase Engineering of Zirconia Support Promotes the Catalytic Dehydrogenation of Formic Acid by Pd Active Sites

The development of Pd-based catalysts with outstanding activity and stability can further promote the hydrogen storage application of formic acid (FA). Regulating the support structure is an effective strategy for enhancing active sites in heterogeneous catalytic systems. This study prepared three types of nanosized ZrO2 through phase engineering to support Pd metal and investigated the implications of support structure on the microenvironment of active sites, thus revealing the structure-activity relationship of the catalysts. The hollow nanoframes like Pd/ZrO2-F with a moderate t-ZrO2 content exhibit remarkable stability and catalytic performance with a TOF of 1348 h-1 at an ambient temperature. Density functional theory (DFT) calculations verify that the crystal phase of ZrO2 can dramatically affect the metal-support interaction and change the Pd electronic state. Moreover, the dehydrogenation energy profiles reveal the synergy effect between ZrO2 phases on Pd active sites in the reaction. Pd/m-ZrO2 is more conducive to the dissociation of FA, and Pd/t-ZrO2 has energy advantages in hydrogen recombination. This work provides a new perspective for understanding the synergistic effect of the zirconia crystal phase on formic acid dehydrogenation by Pd active sites.

Probing the Metal/Oxide Interface of IrCoCeOx in N2H4·H2O Decomposition: An Experimental and Computational Study

Understanding the structure of a functional catalyst is crucial to disclosing the complexity of heterogeneous processes and improving their efficiency. Herein, coprecipitated cobalt-ceria (CoCeOx) oxides doped with Ir (IrCoCeOx) were synthesized and used to assess the performances of metal/oxide interfaces in the N2H4·H2O decomposition performed in aqueous NaOH. Kinetic experiments in batch showed that CoO is the active phase of CoCeOx and that the copresence of Ir and Co (IrCoCeOx) enhanced H2 productivity. A comprehensive characterization (X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy) combined with robust computational modeling based on the density functional theory was employed to attribute the IrCoCeOx performance enhancement to the Ir/CoO metal/oxide interface, the active site of the reaction. On these sites, the improved H2 productivity in the presence of aqueous NaOH was studied operando through modulated excitation-attenuated total reflectance infrared coupled with phase sensitive detection. The formation of surface Co-hydroxyl and -imido groups at the Ir/CoO interface induced the preferential breakage of the N-H bond of N2H4·H2O, favoring the production of H2.

Computational Studies on Microreactors for the Decomposition of Formic Acid for Hydrogen Production Using Heterogeneous Catalysts

Sustainable alternatives to conventional fuels have emerged recently, focusing on a hydrogen-based economy. The idea of using hydrogen (H₂) as an energy carrier is very promising due to its zero-emission properties. The present study investigates the formic acid (FA) decomposition for H₂ generation using a commercial 5 wt.% Pd/C catalyst. Three different 2D microreactor configurations (packed bed, single membrane, and double membrane) were studied using computational fluid dynamics (CFD). Parameters such as temperature, porosity, concentration, and flow rate of reactant were investigated. The packed bed configuration resulted in high conversions, but due to catalyst poisoning by carbon monoxide (CO), the catalytic activity decreased with time. For the single and double membrane microreactors, the same trends were observed, but the double membrane microreactor showed superior performance compared with the other configurations. Conversions higher than 80% were achieved, and even though deactivation decreased the conversion after 1 h of reaction, the selective removal of CO from the system with the use of membranes lead to an increase in the conversion afterwards. These results prove that the incorporation of membranes in the system for the separation of CO is improving the efficiency of the microreactor.

Enhanced stability of sub-nanometric iridium decorated graphitic carbon nitride for H2 production upon hydrous hydrazine decomposition

Stabilizing metal nanoparticles is vital for large scale implementations of supported metal catalysts, particularly for a sustainable transition to clean energy, e.g., H₂ production. In this work, iridium sub-nanometric particles were deposited on commercial graphite and on graphitic carbon nitride by a wet impregnation method to investigate the metal-support interaction during the hydrous hydrazine decomposition reaction. To establish a structure-activity relationship, samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic performance of the synthesized materials was evaluated under mild reaction conditions, i.e. 323 K and ambient pressure. The results showed that graphitic carbon nitride (GCN) enhances the stability of Ir nanoparticles compared to graphite, while maintaining remarkable activity and selectivity. Simulation techniques including Genetic Algorithm geometry screening and electronic structure analyses were employed to provide a valuable atomic level understanding of the metal-support interactions. N anchoring sites of GCN were found to minimise the thermodynamic driving force of coalescence, thus improving the catalyst stability, as well as to lead charge redistributions in the cluster improving the resistance to poisoning by decomposition intermediates.

Formic Acid Dehydrogenation over Ru- and Pd-Based Catalysts: Gas- vs. Liquid-Phase Reactions

Formic acid has recently been revealed to be an excellent hydrogen carrier, and interest in the development of efficient and selective catalysts towards its dehydrogenation has grown. This reaction has been widely explored using homogeneous catalysts; however, from a practical and scalable point of view, heterogeneous catalysts are usually preferred in industry. In this work, formic acid dehydrogenation reactions in both liquid- and vapor-phase conditions have been investigated using heterogeneous catalysts based on mono- or bimetallic Pd/Ru. In all of the explored conditions, the catalysts showed good catalytic activity and selectivity towards the dehydrogenation reaction, avoiding the formation of undesired CO.

Pd–Au Bimetallic Catalysts for the Hydrogenation of Muconic Acid to Bio-Adipic Acid

The hydrogenation reaction of muconic acid, produced from biomass using fermentative processes, to bio-adipic acid is one of the most appealing green emerging chemical process. This reaction can be promoted by catalysts based on a metal belonging to the platinum group, and the use of a second metal can preserve and increase their activity. Pd–Au bimetallic nanoparticle samples supported on high-temperature, heat-treated carbon nanofibers were prepared using the sol immobilization method, changing the Pd–Au molar ratio. These catalysts were characterized by TEM, STEM, and XPS analysis and tested in a batch reactor pressurized with hydrogen, where muconic acid dissolved in water was converted to adipic acid. The synthesized Pd–Au bimetallic catalysts showed higher activity than monometallic Au and Pd material and better stability during the recycling tests. Moreover, the selectivity toward the mono-unsaturated changed by decreasing the Pd/Au molar ratio: the higher the amount of gold, the higher the selectivity toward the intermediates.