Fillipe A.C. Garcia

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

Este trabalho descreve detalhadamente o efeito da quantidade de cerio na estrutura e morfologia da zeolita NH4USY. Ce-USY (2-25% m/m de CeO2) foi obtido por impregnacao umida de CeCl3 seguida de calcinacao a 550oC por 8 h. Em quantidades baixas (2-10%), foi observado que as especies de cerio encontram-se nas posicoes de troca ionica na rede, enquanto em maiores teores (15-25%) pequenos agregados formaram-se na superficie da HUSY. Difratometria de raios X (XRD) mostrou apenas reflexoes relacionadas a HUSY, confirmando a alta dispersao das especies de cerio, porem as analises por espectroscopia Raman com transformada de Fourier (FT-Raman) detectaram CeOx para os materiais acima de 10%. A reacao do CeCl3 com NH4USY produziu NH4Cl, o qual se decompoe em HCl, ocasionando a desaluminizacao da rede. Os materiais apresentaram um aumento da razao Lewis/Bronsted com o aumento da quantidade de cerio, devido a interacao do excesso de cerio com os grupos OH da USY e consequente formacao de especies CeOx.

Síntese e caracterização de mulita utilizando sílica obtida da casca de arroz

Mullite, composed of 1,4Al2O3.SiO2 was synthesized using commercial α-alumina (Alpha Cesar Company) and silica obtained from the calcinations of rice husk. This silica exhibits a high specific surface area, high purity and small average particle diameter. Silica (26.2 wt.%) and α-alumina powders (71.8 wt. %) were mixed and homogenized using an alumina orbital disc mill before and after the calcinations at 1100oC for 4 h in an air atmosphere. Then, the powders were pressed uniaxially at a pressure of 1200 MPa. The green compacts were sintered at 1650oC, for 4 h, in air. The density of compacted sintering samples was determined using the hydrostatic method. The chemical and structural properties were observed using ICP (Inductively Coupled Plasma), XRD (X-ray diffraction) and 29Si MAS (Magic Angle Spinning) NMR (Nuclear Magnetic Resonance) and the microstructural characterization performed using SEM (Scanning Electron Micrography). The results show that it is possible to synthesize mullite ceramic of high-purity and with little glassy phase from the α-alumina and silica obtained from the rice husk that is purified and calcinated.