Effect of Promoters and Calcination Temperature on Surface and Acidity of Modified Zirconia

The effect of sulfating agent concentration, calcination temperature, and Ni incorporation on commercial zirconia have been evaluated. Sulfation of commercial zirconia was prepared by wet impregnation with different amounts of sulfuric acid (0.2, 0.5 and 0.8 M) then calcined at 400, 500, 600, 700, 800 and 900°C for 4 h. Ni was incorporated by refluxing over sulfated zirconia, followed by calcination-reduction process. All samples were characterized by XRD, FTIR, ammonia sorption, SEM-EDX, TEM, and AAS. The presence of sulfate has been added to acidic strength of the sulfated zirconia, the more sulfuric acid were used the stronger the acidic property. There has been degradation of sulfate groups that was adrift in sulfated zirconia by calcination treatment above 600°C. The best physicochemical properties of sulfated zirconia were modification with 0.8 M sulfuric acid and on calcination at 400°C. The 0.8SZ-400 has exhibited the highest Brønsted acidic sites with total acidity of 1.71 mmol/g. The impregnation of Ni enhanced the Lewis acidic sites on the surface of the 0.8SZ-400 which NiSZ gave 2.71 mmol/g of total acidity. All prepared materials consisted of nearly spherical shape of nanocrystal with mostly aggregated particles.

Fabrication of sulfated nanofilter membrane based on carboxymethyl cellulose

The aim of this study is to prepare sulfated carboxymethyl cellulose (SCMC) nanofilter membrane using sulfur trioxide pyridine complex (SO3/pyridine) as sulfating agent and glutaraldehyde (GA) as a crosslinking agent onto polysulfone supporting membrane. The prepared nanofilter was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy and zeta potential. To evaluate the prepared nanofilter, various amounts of SO3/Pyridine were used and efficiency of them was investigated. The results showed that increasing the sulfate groups raised the flux from 13.87 to 29.54 L/(m2·h−1), whereas percentage rejection was increased during the separation of salt aqueous solutions and then decreased. It can be concluded that, SCMC-GA-2 (with molar ratio of SO3/pyridine to CMC of 1) shows high separation efficiency in acidic conditions and improves the hydrophilicity and charge density of the filter.

Temperature imposed textural and surface synergism affecting the isomerization activity of sulfated zirconia catalysts

Using sulfuric acid as the sulfating agent, two catalyst series were obtained from hydroxide and nitrate precursor with a sulfate loading identical to commercial sulfated hydroxide, i.e., 4.2 mass%. After calcination at 500, 600 and 700?C, all nine samples had various contents of residual sulfates depending on the origin of the catalyst. Accordingly, their surface properties were different, which, together with various textural properties, govern the formation of the active phase and their catalytic activity in the n-hexane isomerization reaction. The dominant activity and yield of mainly mono-branched isomers were attained in reaction at 200?C with a commercially sulfated zirconia catalyst calcined at 500?C. Among the SZ catalyst series synthesized from hydroxide and nitrate, the second according to its activity profile was similar to that of the commercially sulfated one, while samples originating from hydroxide showed some activity only after calcination at 600?C. This is due to the poorer textural properties of the hydroxide series, necessitating a higher calcination temperature in order to promote the simultaneous decomposition of S-containing species and their re-adsorption into the zirconia matrix following interaction and active phase formation. It seems that the tetragonal zirconia phase was not responsible for the catalytic activity but a synergistic effect of the textural properties of the samples and the sulfate loadings, which determine different acid strengths on the catalyst surface.