Nanoestruturas metálicas vazias como a fase ativa em catalisadores suportados e não suportados: optimizando performances através da síntese controlada

This dissertation describes the development of a variety of well-defined nanomaterials based on noble metals displaying hollow interiors followed by their application as heterogeneous catalyst towards different chemical transformations. In this work, we employed a simple and robust galvanic replacement reaction approach and its combination with additional metal deposition over preformed templates using hydroquinone as auxiliary reducing agent. This enabled us to precisely control physicochemical features of the produced nanomaterials for catalytic application such as size, composition, shell thickness, surface morphology, number of surface atoms exposed, nature of exposed surface facets, and plasmon band intensity and position. In addition, we could successfully address a well-established challenge in heterogeneous catalysis by noble metals, which is the fabrication of supported materials in which the metal component presents a uniform dispersion over the entire surface of the support without any detectable agglomeration. To this end, the developed approaches for syntheses were scaled up by more than 100 folds, which enabled us to produce enough amount of particles for the uniform incorporation over the commercial silica support. Interestingly, all produced supported nanomaterials displayed satisfactory catalytic activities towards gas phase oxidation reactions and exceptional stabilities on all procedures, demonstrating that our developed approach may inspire the synthesis of noble metal nanostructures displaying attractive features for catalytic applications and uniform dispersion over solid supports to produce solid supported catalysts. As the nanomaterials obtained in this work displayed controlled and well-defined properties, we could stablish a precise correlation between their catalytic or photocatalytic performances and the physicochemical properties that define them. Thus, we showed that by relatively simple adjustments in the synthesis protocols, a rational maneuvering over properties such as size, shape, surface morphology, and composition can be successfully achieved. This represents a powerful tool for boosting the catalytic performances of hollow nanomaterials towards a variety of chemical transformations with completely distinctive mechanisms and nature. In fact, only a few groups have demonstrated the synthesis in large scale of nanomaterials with truly well-defined shapes and sizes in which these parameters can be tightly controlled. Thus, we believe that this dissertation contributes towards the manufacture of supported catalysts containing well-defined and controlled nanomaterials for applications in practical catalytic systems.Não consta resumo na publicação