Evidence of Intracrystalline Mesostructured Porosity in Zeolites by Advanced Gas Sorption, Electron Tomography and Rotation Electron Diffraction

The small size of micropores (typically <1 nm) in zeolites causes slow diffusion of reactant and product molecules in and out of the pores and negatively impacts the product selectivity of zeolite based catalysts, for example, fluid catalytic cracking (FCC) catalysts. Size-tailored mesoporosity was introduced into commercial zeolite Y crystals by a simple surfactant-templating post-synthetic mesostructuring process. The resulting mesoporous zeolite Y showed significantly improved product selectivity in both laboratory testing and refinery trials. Advanced characterization techniques such as electron tomography, three-dimensional rotation electron diffraction, and high resolution gas adsorption coupled with hysteresis scanning and density functional theory, unambiguously revealed the intracystalline nature and connectivity of the introduced mesopores. They can be considered as molecular highways that help reactant and product molecules diffuse quickly to and away from the catalytically active sites within the zeolite crystals and, thus, shift the selectivity to favor the production of more of the valuable liquid fuels at reduced yields of coke and unconverted feed.

Ultrasound-assisted selective hydrogenation of C-5 acetylene alcohols with Lindlar catalysts

The selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) was performed in the presence of Lindlar catalyst, comparing conventional stirring with sonication at different frequencies of 40, 380 and 850 kHz. Under conventional stirring, the reaction rates were limited by intrinsic kinetics, while in the case of sonication, the reaction rates were 50–90% slower. However, the apparent reaction rates were found to be significantly frequency dependent with the highest rate observed at 40 kHz. The original and the recovered catalysts after the hydrogenation reaction were compared using bulk elemental analysis, powder X-ray diffraction and scanning and transmission electron microscopy coupled with energy-dispersive X-ray analysis. The studies showed that sonication led to the frequency-dependent fracturing of polycrystalline support particles with the highest impact caused by 40 kHz sonication, while monocrystals were undamaged. In contrast, the leaching of Pd/Pb particles did not depend on the frequency, which suggests that sonication removed only loosely-bound catalyst particles.

Artefatos funerários como fontes para a história de ofícios urbanos artesanais

Este artigo descreve o uso de artefatos funerários na reconstituição histórica do processo de trabalho em marmorarias instaladas no município de São Carlos (São Paulo, Brasil), no período 1890-1950. Observação direta e registro fotográfico de artefatos funerários, exame de ferramentas de trabalho e utilização de fontes orais permitiram a reconstituição do processo de trabalho. A composição química de fragmentos de artefatos funerários foi determinada por Difração de Raios X e Microscopia Eletrônica de Varredura, evidenciando matérias-primas e sua combinação e uso no processo de trabalho. Considerando-se as etapas produtivas da indústria de rochas ornamentais (extração, serragem e beneficiamento final), os artefatos funerários indicam que as marmorarias inseriam-se na etapa de beneficiamento final. As marmorarias integravam os setores de base técnica artesanal da indústria brasileira, apresentando: baixo grau de concentração de capital e de operários; predomínio da habilidade do ofício especializado; separação pouco nítida entre trabalhadores e instrumentos de trabalho; identificação do trabalhador com o produto. Artefatos de mármore e granito eram destinados a brasileiros de segmentos sociais abastados, durante o início da imigração na cidade de São Carlos (final do século XIX). A partir de 1920, italianos incorporam-se a clientela dos marmoristas, indicando a mobilidade social do imigrante na cidade.