Doctor Educationis / Energy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT). / 2023-12-02

Philosophiae Doctor - PhD / Energy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading-edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT). / 2023-12-01

[pt] Esta tese descreve a síntese de um óxido misto de Zn e Zr (ZnxZr1-xOy), mediante uma técnica ainda não reportada e a utilização deste material na síntese de acetona a partir de etanol. O objetivo foi desenhar um catalisador com propriedades óxido-redutoras e capacidade de se autorregenerar após cada ciclo. A zircônia monoclínica (m-ZrO2) é um óxido já usado em catálise devido às suas propriedades ácido-básicas, mas com fracas propriedades óxido-redutoras. Estas últimas poderiam ser promovidas mediante dopagem substitucional deste material. A inserção de pequeníssimas quantidades de Zn na rede da m-ZrO2, mostraram um incremento apreciável na sua redutibilidade. O material obtido foi caracterizado por diversas técnicas e testado na obtenção de acetona a partir de etanol. O resultado indicou que a dopagem permitiu a formação de vacâncias de oxigênio, as quais promoveram a mobilidade do oxigênio até a superfície e, com isso, aumentaram redutibilidade do material. A seletividade da reação de conversão de etanol teve como produto maioritário a acetona. Foi demostrado que a regeneração do catalisador se deve a espécies oxidantes provenientes da dissociação da água presente no médio reacional; esta dissociação ocorreu nas vacâncias superficiais. Assim, demonstrou-se que a técnica desenvolvida no presente estudo, além de simples, resultou efetiva na síntese do óxido misto de Zn e Zr, um catalisador de composição simples, capaz de conduzir os diferentes passos do mecanismo na síntese de acetona. Considera-se que esta é a primeira etapa na sua viabilização comercial. / [en] This thesis describes the synthesis process of a mixed oxide with Zn and Zr (ZnxZr1-xOy), through a not yet published technique, as well as the utilization of this material in the acetone synthesis from ethanol. The mean goal was to design a catalyst with enhanced oxy-reduction properties and capability for selfregeneration after each cycle. Monoclinic zirconia (m-ZrO2) is already used in catalysis due to its acidic-basic properties, although its oxy-reduction properties are negligible. The enhancement of the oxy-reduction properties can be reached by substitutional doping of this material with a lower oxidation state metal. The insertion of very small quantities of Zn in the m-ZrO2 lattice, showed a high increment of its reducibility. The mixed oxides obtained were characterized by several techniques and catalytically tested in the acetone synthesis from ethanol. The results showed that doping allows the formation of oxygen vacancies, which allow oxygen mobility and therefore, the enhancement of reducibility. The reaction selectivity had acetone as majority product. It was shown that water is also produced and that it is dissociated in the oxygen vacancies generating oxidant species. The catalysts regeneration occurs due to those oxidant species. Therefore, it was demonstrated that the technique developed in this study was easy and effective in the synthesis of the mixed oxide with Zn and Zr, a catalyst with simple composition able to conduct every step of the acetone synthesis. This is considered the first step in the commercial feasibility of this material.