No abstract

No abstract

The amorphous SiO2–Al2O3 supports (SA-x) with different SiO2 weight ratios (x) were prepared by a sol–gel method. The NiW active components were loaded over the supports using an organic matrix combustion method. Semirefined 56# wax was used as the model feedstock of F-T synthetic wax for hydrocracking in a single fixed-bed reactor. The started reaction was conducted at the temperature of 380 °C, 3.5 MPa of pressure, WHSV = 1 h–1, and H2/wax = 0.12 wt/wt. Acidities of the catalysts were determined by TPD-NH3, and the results indicated that the SA-0.4 sample had the highest yield of middle distillate and a promising conversion rate that had a good relation with the strength of the medium acid sites. TEM showed that metal was dispersed very well on the supports using the organic matrix combustion method. Further, SA-0.4 supports were modified with H-β and HZSM-5 zeolites materials and were prepared with different reaction conditions. The prepared supports were denoted as β-SA-y and HZSM-SA-z, respectively, where y and z represent the weight percentage of β zeolite and HZSM-5 zeolite. It was found that β-SA-0.2 had comparable results with SA-0.4 samples, while the reaction temperature was 60 °C lower. The HZSM-SA-z series catalysts showed higher activity, whereas the selectivity of middle distillates was significantly lower, and the yield of gas was too high.

The demand for advanced materials in modern industry and technologies is increasing, because pure metals and simple alloys can not meet the needs of society. Metal matrix composites (MMCs) are advanced materials that have been one of the hot fields of materials research. [1,2] MMCs, especially aluminum-and titanium-based materials, have a high potential for advanced structural applications in which high specific strength and modulus, as well as good elevated-temperature resistance, are important. Particulatereinforced MMCs are of special interest because of their ease of fabrication, low cost, and more isotropic properties. The properties of MMCs are controlled by the size and volume fraction of the reinforcement phase as well as by the nature of the matrix±reinforcement interface: an optimum set of mechanical properties tends to be obtained when fine and thermally stable ceramic particulates are dispersed in a metal matrix.Traditionally, MMCs have been produced by processing techniques such as powder metallurgy, [1,2] preform infiltration, [3] spray deposition, mechanical alloying, and various casting technologies, such as squeeze casting, rheocasting, and compocasting. [4±8] Such methods are based on the addition of the particulate reinforcement to the matrix material in molten or power form. The scale of the reinforcing phase is limited by the starting-power size, which is typically of the order of microns to tens of microns, and rarely less than 1 lm.In traditional MMC processing it is often necessary to improve the wetting between the molten metal and the particulate (which is typically poor) in order to obtain a good bond between the matrix and reinforcement. This problem can be resolved by adding a strongly reactive alloying element such as Mg or Li, or by coating the particulate. Mechanical stirring or pressure infiltration can also be helpful. Other difficulties, such as uneven distribution of reinforcements, interfacial reactions between the matrix and reinforcements, and control of volume fraction are often encountered during the fabrication of MMCs. Such factors can adversely affect the properties of the product.In recent years, new processing techniques based on in situ production of MMCs have emerged. In situ techniques involve a chemical reaction resulting in the formation of a very fine and thermodynamically stable reinforcing ceramic phase within a metal matrix. As a result, this provides thermodynamic compatibility at the matrix±reinforcement interface. The reinforcement surfaces are also likely to be free of contamination and, therefore, a stronger matrix±dispersion bond can be achieved. Some of these technologies include DIMOX TM , XD, PRIMEM TM , reactive gas infiltration, hightemperature self-propagating synthesis (SHS), liquid±solid or solid±gas±liquid reactions, [9±14] and plasma in situ MMCs. [15] Thus in situ composites are a new topic of interest in MMC research. They have some advantages over traditional MMCs, such as excellent interfacial bonding and easy production technology....