Nanosized transition metals in controlled environments of phyllosilicate-mesoporous silica composites as highly thermostable and active catalysts.

Stabilization of transition metals in nano-phyllosilicate phases generated by digestion of mesoporous silica is reported as an efficient route for the formation of highly dispersed metallic nanoparticles with outstanding catalytic activity.

Composition-dependent morphostructural properties of Ni-Cu oxide nanoparticles confined within the channels of ordered mesoporous SBA-15 silica.

NiO and NiO-CuO polycrystalline rodlike nanoparticles were confined and stabilized within the channels of ordered mesoporous SBA-15 silica by a simple and viable approach consisting in incipient wetness impregnation of the calcined support with aqueous solutions of metal nitrates followed by a mild drying step at 25 °C and calcination. As revealed by low- and high-angle XRD, N2 adsorption/desorption, HRTEM/EDXS and H2 TPR analyses, the morphostructural properties of NiO-CuO nanoparticles can be controlled by adjusting their chemical composition, creating the prerequisites to obtain high performance bimetallic catalysts. Experimental evidence by in situ XRD monitoring during the thermoprogrammed reduction indicates that the confined NiO-CuO nanoparticles evolve into thermostable and well-dispersed Ni-Cu heterostructures. The strong Cu-Ni and Ni-support interactions demonstrated by TPR and XPS were put forward to explain the formation of these new bimetallic structures. The optimal Ni-Cu/SBA-15 catalyst (i.e., Cu/(Cu+Ni) atomic ratio of 0.2) proved a greatly enhanced reducibility and H2 chemisorption capacity, and an improved activity in the hydrogenation of cinnamaldehyde, as compared with the monometallic Ni/SBA-15 or Cu/SBA-15 counterparts, which can be associated with the synergism between nickel and copper and high dispersion of active components on the SBA-15 host. The unique structure and controllable properties of both oxidic and metallic forms of Ni-Cu/SBA-15 materials make them very attractive for both fundamental research and practical catalytic applications.

Hydrogenation of Unsaturated Carbonyl Compounds on non-Calcined LDHs. I. Synthesis and Characterization of ZnNiCuAl Hydrotalcite-like Materials.

Several Zn/Ni/Cu/Al layered double hydroxides (LDH) with variable Ni/Cu ratios but constant Zn/Al, as well as M2+/M3+ ratios, were synthesized by coprecipitation method with CO32- as compensating anion. The main goal of the study was to investigate the influence of the catalysts composition, especially Ni/Cu ratio, on the physical and catalytic properties of these materials. The XRD results show that all the LDHs samples are well crystallized and contain only pure phases. Moreover, the spectral techniques (FT-IR and DR-UV-VIS) indicated that both Ni and Cu species are present in the brucite-like layers of LDHs. The shape of the nitrogen physisorption isotherms obtained at -196 °C indicates a predominantly mesoporous materials; the surface areas and pore volumes are in the specific ranges between 37-86 m2.g-1 and 0.31-0.75 cm3.g-1, respectively. Three characteristic weight losses between 30 and 400 °C are identified by TG analysis for the hydrotalcite-like materials synthesized in this study. Moreover, an influence of the Ni/Cu ratios on the amount of the physisorbed water was noticed. The preliminary catalytic test revealed unusual catalytic properties of the non-calcined samples in the liquid phase hydrogenation of trans-cinnamaldehyde.