| Palladium membranes have drawn increasing attention in recent years due to their good properties, such as good mechanical stability, thermal stability and only permeable to hydrogen. Therefore, as one kind of membrane reactors, Pd membranes have wide applications in hydrogenation, dehydrogenation, H2 separation and purification and some hydrogen related reactions. Especially, the unique property of Pd membrane was illustrated in the direct hydroxylation of benzene to phenol, which made the research of Pd membrane more significant in academic and industry.In this paper, based on the preparation of Pd-ceramic composite membrane, thin dense Pd-silicalite-1 and Pd-TS-1 composite membranes were successfully prepared using conventional electroless plating on macroporousα-Al2O3 substrate. Moreover, in order to increase the stability of Pd membrane and simply the preseeding process of Pd on support in the conventional electroless plating, a novel "co-seedng"method was developed to prepare thin dense composite membranes of excellent stability on macroporousα-Al2O3 supports, and applied in direct synthesis of phenol from benzene. The morphology and hydrogen permeability of the modified support and Pd composite membrane were characterized by means of SEM, XRD, TEM, EDX, XPS, EPMA, FT-IR and high temperature permeation tests. The results will bring on important significance at the side of improving preparation method and increasing the stability of Pd membrane reactor.The thesis mainly includes several aspects as follows:1. Pd-Al2O3 composite membrane was prepared using electroless plating. Some factors on preparation of Pd membrane such as plating time, temperature and support morphology were studied. It indiated that the deposition amount of Pd increased with increasing temperature during 303-333K. The ideal Pd membrane could be obtained at 318K, higher or lower than that temperature would affect the Pd deposition. The reaction performed slower at lower temperature; the higher temperature accelerated reaction, but the Pd particles would congregate seriously. In addition, the longer time for electroless plating favored the deposition of Pd membrane, the uniform and continous Pd membrane could be obtained by elecroless plated for 2 hours. Moreover, the morphology of support played important role in preparation of Pd membrane, it was difficult obtain dense and thin Pd membrane on macroporous support with pore size of 3μm except for modification of the support. 2. In order to improve the topology of macroporousα-Al2O3 supports, silicalite-1(Sil-1) and TS-1 zeolite were adopted, then, dense Pd-zeolite composite membranes were deposited using convenitional electroless plating. It indicated that the morphology of zeolite layer plays important role in performance of Pd membranes. The Sil-1 zeolite layer with smoother surface was bad for preparing Pd membrane, which led to decrease the adhesion between Pd layer and modified support. The Sil-1 layer with thickness of 2μm obtained by hydrothermal synthesis favored the preparation of dense Pd membrane. The H2 permeance and H2/N2 ideal selectivity for the Pd-Sil-1 composite membrane at 773 K were 1.2×10-6 mol·m-2·s-1·Pa-1 and 420, respectively. In addition, continous Pd-TS-1 composite membrane was obtained using above method. The H2 permeance and H2/N2 ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10-7 mol·m-2·s-1·Pa-1 and 310, respectively.3. CS-Pd-silicalite-1(CS-Pd-Sil-1) and CS-Pd-TS-1 composite membranes prepared by "co-seeding" method had good H2 permeability and excellent stability. Herein, the Pd/zeolite"co-seeds" were served as seed roles both for growth of zeolite silicalite-1 layer on the support and for Pd membrane deposition. The deposition process of Pd membrane was studied; it indicated that the Pd growth starts from the zeolite seed layer, filling the inter-zeolite pores before forming a Pd film on the surface of the zeolite layer; the Pd layer anchored in the zeolite layer, which was good for increasing the Pd membrane stability. The micro structure and thickness of zeolite layer were the key roles. Adjusting the growth of Sil-1 zeolite, the ideal CS-Pd-Sil-1 composite membrane could be prepared on the silicalite layer with thickness of 2μm. The H2 permeance and H2/N2 ideal selectivity for the CS-Pd-Sil-1 composite membrane were 1.78 x10-6 mol·m-2·s-1·Pa-1 and 1280 at 773 K, respectively. The CS-Pd-silicalite-1 composite membrane was stable over a period of 200 h under hydrogen permeation and 18 gas-exchanging cycles between H2 and N2 at 623K and over 15 pressure cycles between 100 kPa and 20 kPa at 773K. Moreover,15 temperature cycles between 673K-773K and 10 gas-exchanging cycles between H2 and N2 at 473K didn't impair the hydrogen permeation flux. In the same way, the CS-Pd-TS-1 composite membrane with good stability was prepared. The H2 permeance and H2/N2 ideal selectivity for the CS-Pd-TS-1 composite membrane were 5.3x10-7 mol·m-2·s-1·Pa-1 and 450 at 773 K, respectively. Moreover, the hydrogen permeability was stable after 15 temperature cycles between 673～773 K.4. Direct hydroxylation of benzene to phenol was performed in the CS-Pd-silicalite-1 composite membrane reactor at temperature from 423 to 523K. The H2/O2 ratio and reaction temperature were investigated. The degree of hydrogenation of benzene was remarkable at higher temperature or higher H2/O2 ratio, which affected phenol yield. Both H2 conversion and water generation rate increased with decreasing H2/O2 ratio.An appropriate H2/O2 ratio of 4.7 was optimized, in which the benzene conversion was 5.06%, correspondingly the phenol selectivity was 60.81%. Moreover, the formation process of water was analyzed based on the relationship between the water generation rate and H2 conversion, it indicated that the water was formed on the surface of Pd membrane mainly from H2 reacted with O2. In addition, the CS-Pd-Sil-1 membrane kept stable for 46 h operation in the reaction at 473K.
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