Sulfated TiO2 Catalysts Research Articles

Iron oxide supported sulfated TiO2 nanotube catalysts for NO reduction with propane

Sulfated TiO2 nanotubes and a series of iron oxide loaded sulfated TiO2 nanotubes catalysts with different iron oxide loadings (1wt%, 3wt%, 5wt% and 7wt%) were prepared and calcined at 400°C. The physico-chemical properties of the catalysts were studied by using XRD, N2-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H2-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO2 nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500°C. Highest activity (90% NO conversion) was observed with 5wt% iron oxide supported on sulfated TiO2 catalyst at 450°C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50h of reaction.

Performance Evaluation of Sulfated-TiO2 as a Modifier to Co−Ni−ZrO2 Catalyst in a Dual-Bed Reactor for the Selective Production of C4 Hydrocarbons from Syngas

Modified Fischer−Tropsch (MFT) synthesis was performed at atmospheric pressure in a fixed-bed microreactor with a dual-bed configuration using Co−Ni−ZrO2 and sulfated-TiO2 solid acid catalysts. The sulfate loading in the sulfated-TiO2 catalyst was in the range 5−15 wt % whereas sulfated-TiO2 to Co−Ni−ZrO2 catalyst mass ratio was 1−3. The catalyst system was activated by reduction at temperatures ranging from 573 to 723 K for 16 h whereas sulfated-TiO2 catalyst was calcined at temperatures in the range 723−923 K for 4 h. MFT reactions were performed at weight hourly space velocities (WHSV) in the range 5−20 h-1 and reaction temperatures ranging from 513 to 533 K. Though these parameters did not have substantial effects on the hydrocarbon product composition, the optimum selectivities for C5+ hydrocarbons, i-C4 hydrocarbons, and C2−C4 olefins from syngas using Co−Ni−ZrO2 due to the presence of the modifier sulfated-TiO2 were increased from 26 to 31 wt %, 2 to 4 wt % and 34 to 44 wt %, respectively. However, the presence of sulfated-TiO2 catalyst had no substantial effect on the selectivity for total C4 hydrocarbons. Though the sulfated-TiO2 catalysts possessed large amounts of acid sites, these sites were weak, and as such, could only catalyze reactions such as isomerization, oligomerization, dehydrogenation and alkylation. The more demanding cracking reactions could not be promoted on sulfated-TiO2 catalysts. The weak acidity exhibited by sulfated-TiO2 catalysts is an asset in that it was able to maintain activity stability for a long period of time in contrast to the performance of sulfated-ZrO2 catalysts, which deactivated rapidly because of its strong acid sites.

Catalytic Hydrolysis of Dichlorodifluoromethane (CFC-12) on Sol-Gel-Derived Titania Unmodified and Modified with H2SO4

Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) in a humid air stream was studied over pure and sulfate promoted TiO2catalysts which were prepared by sol-gel methods. The results showed that complete conversion of CFC-12 on unmodified TiO2was achieved at reaction temperatures higher than 340°C under the employed reaction conditions. The selectivity to CO2([CO2]produced/[CFC-12]converted) varied from 0.5 to 0.88 over the range of 250–350°C and CClF3(CFC-13) was detected as the main by-product. Surface fluorination of the TiO2catalyst during the reaction improved its activity, induced the formation of the fluorinated by-product CFC-13, and changed such properties of the catalyst as its specific surface area, pore size distribution, and crystal size. It was found that the catalytic and structural properties of TiO2were greatly improved by sulfation. The sulfated TiO2(TiO2/SO42−) exhibited excellent reaction activity and selectivity for CFC-12 catalytic decomposition at low reaction temperatures (190–250°C) while retaining a stable structure. Complete decomposition of CFC-12 with stoichiometric production of CO2was observed over the TiO2/SO42−catalyst at 250°C under otherwise identical reaction conditions as used for pure TiO2. Results of catalyst characterization by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and N2sorption analysis indicated that surface sulfate species formed on the sulfated TiO2. When compared to unmodified TiO2, the sulfated TiO2exhibited higher resistance to crystal phase transformation from anatase to rutile, higher resistance to the deleterious effects of fluorination of the catalyst, and higher specific surface area. Fluorination of the catalyst did not improve the activity of sulfated TiO2and no CFC-13 was detected as a by-product, indicating that fluorine was not involved in the formation of reaction sites over the sulfated TiO2catalysts.