Preparation of nanocrystalline γ-Al_2O_3 catalyst using different procedures for methanol dehydration to dimethyl ether

A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method （sample A）, precipita-tion method （sample B） and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide （CTAB） as templates （samples C and D, respectively）. Textural and acidic properties of γ-alumina samples are characterized by XRD, N2 adsorption-desorption and NH3-TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH3-TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.

Synthesis of Cobalt Chromite Nanoparticles by Thermolysis of Mixed Cr^(3+) and Co^(2+) Chelates of 2-Mercaptopyridin N-Oxide

Pure greenish-blue cobalt chromite(Co Cr/_2O_4) nanoparticles with narrow particle range of 4.1±1.9nm and surface area of 78.2 m2·g-1were synthesized through mixed chelates thermolysis of corresponding metals using 2-Mercaptopyridine N-oxide sodium salt as chelating agent. During the thermolysis procedure,high amount of gases were emitted that led to the formation of nanoparticles with high surface area. The product was characterized by TGA, DTG, XRD, TEM, SEM, LLS, BET and chemical analysis. Design of experiments was performed to fulfill the two levels L_4 Taguchi design. It was found that the temperature and time of thermolysis process have significant effect on the particle size reduction. The Oxidation of trichloroethylene was carried out over Co Cr_2O_4 nanocrystallite. Catalytic activity analysis revealed that the synthesis Co Cr_2O_4 possesses high catalytic activity for this process.