UCLA

Worldwide efforts have been focused to introduce greener chemical and energetic processes that drive the society away from the dependency on fossil fuels, looking to reduce the environmental footprint of modern societies. Catalysis for instance, has been for decades the winning technology which helps to improve the efficiency of processes in petrochemical, pharmaceutical, and biomedical industries to mention a few. Efficiency of catalysts come mostly from its structure and composition which proportionate high activity and selectivity. However, the use of expensive noble metals as catalyst materials remains a key issue for industrial applications. Thus, developing materials that reduce and mitigate carbon dioxide emissions as well as decrease of waste of the materials using during these processes remain a tremendous challenge to overcome. Nanotechnology for instance, is a growing technology with great impact in the industrial,pharmaceutical and energetical sectors. In fact, nanomaterials provide a better economical option, less waste and still with superior performance than their bulk counterparts which is explained from their reduce size, shape and larger surface areas which leads to overall higher catalytic performance. Nanocatalysis modify the rate of a chemical reaction by speeding up or accelerating the reaction rate without being consumed, making the process more energetically favored. Nanocatalyst have significant impact in different industrial processes as chemical reactions to produce fine chemicals, or for renewable energy and among others. As it was mentioned previously, the high performance of nanocatalyst is associated with the atoms at the surface of the nanostructure which are known as the active sites for catalysis. Moreover, it is well known that surface atoms placed at the corner or edges of the nanocatalyst are more active than those surface atoms at planes, and it the same manner with surface-to-volume ratio, their number will increase with decrease of particle size. In addition to nanoparticle size, crystallographic facets lead to different shapes or morphologies which are also contributing to the number of atoms at the surface, edges and corners. All of these contributing together to the efficiently performance of nanocatalyst for the target reactions . In this thesis is presented nanocatalyst materials development, and studies about their synergetic effect of the different components for heterogeneous catalytic applications.

First, benzaldehyde byproduct is an intermediate in the production of fine chemicals and additives. Tuning selectivity to benzaldehyde is therefore critical in alcohol oxidation reactions at the industrial level where the typical methods employ toxic oxidant chemicals for its production. Herein, we report a simple but innovative method for the synthesis of palladium hydride and nickel palladium hydride nanodendrites with controllable morphology, high stability, and excellent catalytic activity. The synthesized dendrites can maintain the palladium hydride phase even after their use in the chosen catalytic reaction. Remarkably, the high surface area morphology and unique interaction between nickel-rich surface and palladium hydride (β-phase) of these nanodendrites are translated in an enhanced catalytic activity for benzyl alcohol oxidation reaction. Our Ni/PdH0.43 nanodendrites demonstrated a high selectivity towards benzaldehyde of about 92.0% with a conversion rate of 95.4%, showing higher catalytic selectivity than their PdH0.43 counterparts and commercial Pd/C. The present study opens the door for further exploration of metal/metal-hydride nanostructures as next-generation catalytic materials.

Second, palladium hydride system (PdHx) has been of great interest primarily due to the high solubility of hydrogen on the palladium fcc (Pd-face centered cubic) lattice which make them suitable candidates as environmental friendly materials for applications in terms of storage and use of energy, having specific relevance in hydrogen storage, fuel cell, batteries, kinetics reversibility studies, and more. Palladium hydride properties do not only include adsorption and desorption of hydrogen, but they are also effective for electrocatalytic applications. Overall, palladium hydride and its alloys properties are strongly correlated with their electronic and crystal structure changes. Thus, a deep understanding and methodology for their production is crucial for their use in the mentioned applications. Despite of the studies found in literature, there is still a lack of studies for direct but simple synthesis of palladium hydride with practical applications. For instance, palladium hydride literature studies are mostly based on in-situ studies where a limitation of sample, stability and reproducibility are some of the major problems associated with them which also leads to a lack of studies related to their properties and how to tune them. Herein, we reported a simple yet well designed method for the synthesis of stable β palladium hydride with different morphologies and decoration of its surface with organic ligands which lead to different effects in terms of nanocrystal sizes and the ability of tune of its properties. Upon the use of different capping agents during the synthesis, diverse magnetic properties have arisen, as well as an increase in their hydrogen storage capacity. These properties are found to be different from their counterpart of pure palladium and palladium hydride material without coating agents.

Third, developing non-platinum materials with enhance performance for electrocatalytic reactions has been gaining attention in recently years. Palladium and Palladium-based materials are the most suitable candidates to substitute platinum catalysts in anodic and cathodic reactions. Here we developed a facile path to synthesize PdCu nanowires having alloy and intermetallic phases within their structures. To the best of our knowledge, the catalytic properties of *PdCu intermetallic nanowires for hydrogen evolution reaction and formic acid oxidation reaction are higher than their PdCu alloy counterpart and those previously reported for 0D and 1D bimetallic nanostructures. Tafel slopes and overpotential presented here during hydrogen evolution reaction of *PdCu NWs in both acidic and basic conditions are superior than PdCu alloy nanowires, Pd nanowires and comparable to commercial Pt. In terms of formic acid oxidation reaction, *PdCu NWs also exhibits the highest mass activity, followed by PdCu alloy NWs, and being both superior than commercial Pd. In addition, PdCu nanowires also exhibit superior stability for both reactions: hydrogen evolution reaction in acid and basic conditions, and formic acid oxidation reaction as well as good resistance against CO poisoning. Density functional theory (DFT) calculations demonstrate that the improved HER performance at acidic condition is due to the decrease in the hydrogen binding energy of the compressed PdCu-B2 phase, and the improved HER performance at alkaline condition is due to the reduced water dissociation barriers at alkaline condition of *PdCu intermetallic phase.