RESUMO
The performance of catalysts prepared from hierarchical Y zeolites has been studied during the conversion of vacuum gas oil (VGO) into higher-value products. Two different catalysts have been studied: CatY.0.00 was obtained from the standard zeolite (Y-0.00-M: without alkaline treatment) and CatY.0.20 was prepared from the desilicated zeolite (Y-0-20-M: treated with 0.20 M NaOH). The cracking tests were carried out in a microactivity test (MAT) unit with a fixed-bed reactor at 550 °C in the 20-50 s reaction time range, with a catalyst mass of 3 g and a mass flow rate of VGO of 2.0 g/min. The products obtained were grouped according to their boiling point range in dry gas (DG), liquefied petroleum gas (LPG), naphtha, and coke. The results showed a greater conversion and selectivity to gasoline with the CatY.0.20 catalyst, along with improved quality (RON) of the C5-C12 cut. Conversely, the CatY.0.00 catalyst (obtained from the Y-0.00-M zeolite) showed greater selectivity to gases (DG and LPG), attributable to the electronic confinement effect within the microporous channels of the zeolite. The nature of coke has been studied using different analysis techniques and the impact on the catalysts by comparing the properties of the fresh and deactivated catalysts. The coke deposited on the catalyst surfaces was responsible for the loss of activity; however, the CatY.0.20 catalyst showed greater resistance to deactivation by coke, despite showing the highest selectivity. Given that the reaction occurs in the acid sites of the zeolite and not in the matrix, the increased degree of mesoporosity of the zeolite in the CatY.0.20 catalyst facilitated the outward diffusion of products from the zeolitic channels to the matrix, thereby preserving greater activity.
RESUMO
The catalytic combustion of diesel soot is addressed with flexible and structured "paper catalysts". Two different series of catalysts were prepared either by drip impregnation or by a spray method to deposit a mixture of Co, Ba, and K or a mixture of Co and Ce onto SiO2-Al2O3 ceramic paper matrixes. In every case, CeO2 nanoparticles were added to bind the ceramic fibers. SEM images showed that the impregnation method generated catalytic particles concentrated as large chunks (> 10 µm), mainly at ceramic fiber crossings, whereas the spray method produced smaller catalytic particles (< 1 µm) well distributed throughout the ceramic paper. Besides, Co-Ba-K particles appeared better dispersed on the surface of ceramic fibers than Co-Ce due to the presence of K. Additionally, FTIR spectra showed the formation of O22- and O2- species associated with CeO2 (binder) on the samples containing potassium which gave the Co-Ba-K-ceramic paper good catalytic properties, thus making the Co-Ba-K drop impregnated the best catalyst both considering activity and stability. Successive temperature programmed oxidation (TPO) runs up to 700 °C caused the formation of cobalt silicates in the catalytic ceramic paper prepared by the spray method, as indicated by TPR. The formation of these species was probably favored by the smaller size of cobalt particulates and their higher dispersion in the catalysts prepared by the spray method. This provoked the partial loss of the redox properties of Co3O4. TPR experiments also indicated the formation of BaCoO3 in Ba-containing ceramic paper, which could help in maintaining the catalyst activity after several TPO runs through the capacity of this mixed perovskite-type oxide to trap and release NOx.