Preparation, Characterization And Application Of Molecular Sieve Membrane Encapsulated Core-shell Catalysts

Core-shell composite materials, which consist of core and external shell, are of great interest in many fields and have many potential applications not only for the combination of two composite materials but also for the following functionalization of composite materials. Molecular sieve membrane encapsulated core-shell catalyst is a kind of catalytic material which consists of zeolite membrane and catalytic materials. Combining the catalytic activity of catalyst and sieving effect of molecular sieve membrane, the core-shell catalyst has some special functions such as improving the activity of catalyst and resistance to poisoning.This paper mainly studied about molecular sieve membrane encapsulated core-shell catalyst with the function of poisoning resistance. Moreover, preparation method, catalytic activity and anti-poison ability of microporous and mesoporous core-shell catalysts have been studied. Preparation methods of core-shell catalysts were developted and optimized to raise the catalytic activity and anti-poison ability. At last the organic sulfides with different molecular sizes were used as probe molecules to test the anti-poison mechanism of the core-shell catalyst and a mathematical model was developed which demonstrated the regulation of ability of core-shell catalysts affected by the shell. There are four parts as follows:1. In Direct Internal Reforming Molten Carbonate Fuel Cell (DIR-MCFC), one of the technical problem is that the internal reforming catalyst which is used as catalyst for methane steam reforming reaction can be poisoned and deactivated by alkali electrolyte (K2CO3:Li2CO3=62:38, molar ratio) in cell. In this paper, the internal reforming catalyst Ni/Al2O3was encapsulated by a layer of silicalite-1(Sil-1) zeolite membrane and formed Ni/Al2O3-Sil-1core-shell catalyst. First, the submicron Sil-1seeds were synthesized by hydrothermal method and jointed to surface of spheric Ni/Al2O3catalysts with silane coupling agent. Based on the Sil-1seeds, the Sil-1shell was formed through secondary grouth method. The effect of synthesis parameters such as synthetic temperature and time were studied and thickness of Sil-1shell was conducted by synthetic time. The Ni/Al2O3-Sil-1has excellent catalytic activity, stability and alkali-resistance property. Alkali-resistance property was controlled by altering the Sil-1shell thickness to meet different alkali-poision conditions.2. To improve the catalytic activity and alkali-resistance ability, parameters of the preparation method of Ni/Al2O3-Sil-1core-shell catalysts were analyzed. It is founded that excessive calcination times of Ni/Al2O3catalysts were the main deactivate reason. A new preparation method was designed to reduce calcination times of Ni/Al2O3catalysts:the nickel was injected to Al2O3carrier which was encapsulated with Sil-1shell in advance. The nickel over-loaded on the surface of Sil-1shell was removed by driven method of toluene. The results of XRD, XRF, TPR and H2-TPD indicate that the new method could avoid the sintering of nickel and improve the performance of core-shell catalysts.3. In addition to the microporous Sil-1shell, the mesoporous MSU-1membrane shell was also synthesized and formed the Ni/Al2O3-MSU-1-S core-shell catalysts to improve the activity and alkali-resistance. Similarly, the submicron Sil-1crystals were first jointed to surface of spheric Ni/Al2O3catalysts with silane coupling agent. Then a continuous and uniform MSU-1membrane was synthesized on the sphere catalyst by surface reaction of silicon condensation which was catalyzed by NaF. Sil-1zeolite was used as a stable transition layer to modify the catalyst surface which could solve the weak bonding force between MSU-1membrane and alumina carrier. The parameters of preparation of Ni/Al2O3-MSU-1-S were studied by XRD, TEM and N2adsorption. Then the NaF was used to conduct the thickness of MSU-1shell. The Ni/Al2O3-MSU-1-S core-shell catalyst has a better catalytic activity and alkali resistance property4. To find the anti-poison mechanism of core-shell catalysts, the organic sulfides with different molecular sizes were used as probe molecules to study the catalytic activity and anti-poison ability of core-shell catalysts with different shell thicknesses and pore sizes. According to the results of experiments, the mathematical model was established to simulate the performance of anti-poison ability and catalytic activity. The simulation results provide the optimum parameters and regulations for the design of core-shell catalysts.