Nanobastões porosos de CeO2-ZrOx decorados com nanopartículas de ouro para a catálise da reação de oxidação preferencial de monóxido de carbono

Author(s)

Raul Bruno Machado da Silva

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2020-01-17

Examining board members

Italo Odone Mazali; Juliana dos Santos de Souza; Pedro Paulo Corbi

• Advisor: Italo Odone Mazali

Abstract

This work brings a novel class of catalysts for the reaction of preferential oxidation of carbon monoxide (PROX-CO) based on ceria nanorods decorated with gold nanoparticles on the surface. A hydrothermal synthesis with several advantages such as a one-step, one-pot, low-cost and easy-to-purify process that enables the preparation of high purity ceria nanoparticles of controlled size and morphology. Afterward, a novel acid lixiviation process based on treating the nanoparticles with sulfuric acid solution was employed in which the native pores of ceria nanorods were expanded improving the total oxygen storage capacity (OSC) of the material, a physical-chemical property of utmost importance to understand chemisorption phenomena in catalysis. Inductively coupled plasma optical emission spectroscopy (ICP-OES) results revealed that the acid leaching conditions employed were effective to expand the pore structure without compromising the facets structure of ceria nanorods and avoiding their dissolution. Raman results confirmed the increase in oxygen vacancies concentration in the lixiviated sample of nanorods. Cerium nanorods were also successfully doped with Zr (IV) ions via a co-precipitation technique. In order to complete the nanohierarchy of the catalyst, gold nanoparticles were placed down onto the oxide surface by the deposition-precipitation (DP) method. In the methodology carried out in this work, gold precursor, HAuCl4, is brought out of the solution in the presence of a suspension onto the support by increasing the pH in order to precipitate Au(OH)3, which gives out metallic gold after thermal treatment. The surface of the support plays a role as a nucleating agent controlling. Different methods to increase the pH of the solution, such as addition of NaOH and thermal decomposition of urea and different annealing temperatures were employed, which led to different catalytic performances. The catalysts composed by lixiviated ceria nanorods were proved to be better for PROX-CO reaction as they increased the total CO conversion and decreased the maximum conversion temperature, which is appropriate for the potential use of this catalyst in fuel cells. The Zr-doped nanorods also were determined to be more effective which was attributed to the capacity of Zr (IV) to improve the oxygen vacancy concentration of the nanorods (AU)

• FAPESP's process: 18/07853-2 - Influence of the structural design of CeO2 porous nanorods decorated with bimetallic nanoparticles upon the optimization of water gas shift reaction
• Grantee: Raul Bruno Machado da Silva
• Support Opportunities: Scholarships in Brazil - Master