Catalytic Activity Of SO Research Articles

Enhanced catalytic activity of SOx-incorporated graphene for the hydrogen evolution reaction

SOx incorporation enhances the catalytic activity of carbon-based nanostructures in the hydrogen evolution reaction (HER).

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO 4 2- /γ-Al2O3) and a cobalt-containing composite (0.5%Сo/SO 4 2- /γ-Al2O3) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C6–C8), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO 4 2- /γ-Al2O3 in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al2O3 promoted by cobalt salt.

De–SO x additives based on mixed oxides derived from Mg,Al-hydrotalcite-like compounds containing Fe, Cu, Co or Cr

Mg,Al-hydrotalcite-like compounds (HTLCs) with an M 3+/(M 2+ + M 3+) molar ratio equal to 0.25 in which Mg or Al were partially replaced by Cu, Co, Cr or Fe were prepared and used as precursors for different mixed oxides (MO): Cu–MO, Co–MO, Cr–MO or Fe–MO. These materials were evaluated for SO x removal under conditions similar to those found in the fluid catalytic cracking (FCC) regenerator. The following order of catalytic activity for SO x uptake was observed: Cu–MO > Co–MO > Fe–MO > Cr–MO. The regeneration of the sulfated additives was also studied and the results showed that the composition of the reductive stream influenced the regeneration profiles, the total quantity of sulfur released, and the reduction products distribution, in a specific way for each sample. These results could be related to the nature of the reducing agent and to the fact that the thermal stability and the reducibility of the sulfates are significantly affected by the metal with redox properties present in the additive.

Direct oxidation of n-heptane to ester over modified sulfated SnO 2 catalysts under mild conditions

The direct oxidation of n-heptane to ester using air as the oxidant under mild conditions assisted by sulfated tin oxide (SO 4 2−/SnO 2) and Co modified sulfated tin oxide (SO 4 2−/SnO 2–Co 2O 3) prepared by chemical co-precipitation method and characterized by means of SEM, XRD, FT-IR and XPS techniques was studied. From the results it was found that the catalytic activity of SO 4 2−/SnO 2–Co 2O 3 is higher than that of SO 4 2−/SnO 2 in this target reaction, and two asymmetric esters: diisobutyl phthalate and cyclohexylmethyl tridecyl oxalate that have not been reported in the directly oxidation of n-heptane by traditional method have been obtained. The possible mechanism was also discussed.

The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al 2O 3 samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al 2O 3 methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO 4 2−/γ-Al 2O 3 for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO 4 2−/γ-Al 2O 3 was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO 2. On the other hand, when the calcination temperature of SO 4 2−/γ-Al 2O 3 increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO 2. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO 4 2−/γ-Al 2O 3 for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO 4 2−/γ-Al 2O 3 with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.

Aqueous Cr(VI) photo-reduction catalyzed by TiO 2 and sulfated TiO 2

TiO 2 and sulfated TiO 2 (SO 4 2−/TiO 2) catalysts with different textural properties were prepared under different calcination temperatures and the photo-reduction of Cr(VI) to Cr(III) catalyzed by these catalysts was investigated. For the photocatalytic reduction of Cr(VI), the photocatalytic activities of the TiO 2 samples were found to be strongly dependent of the calcination temperature and TiO 2 calcined at 400 °C showed a higher catalytic activity compared to other TiO 2 catalysts. In contrast, sulfation of TiO 2 stabilized the catalytic activities of SO 4 2−/TiO 2 catalysts. At low calcination temperature, SO 4 2−/TiO 2 catalysts exhibited catalytic activities almost comparable with that of TiO 2 and the catalytic activities of SO 4 2−/TiO 2 catalysts were markedly higher than TiO 2 under high calcination temperature. In addition, the removal of surface SO 4 2− of SO 4 2−/TiO 2 catalyst led to a marked decrease of the catalytic activity for Cr(VI) photo-reduction, suggesting that the presence of surface SO 4 2− provided an acid environment over the catalyst surface and favored the photo-reduction of Cr(VI).

Synthesis, characterization, and catalytic activity of SO 4/Zr 1− xSn xO 2

The Sn-doped zirconia catalysts, SO 4/Zr 1− x Sn x O 2 ( x=0, 0.05, 0.10, 0.175, 0.25, 0.35), SO 4/ZrO 2, and SO 4/SnO 2, were prepared by hydroxide precipitation. The freeze-dried hydroxides were sulfated with (NH 4) 2SO 4 and calcined at 500 °C for 3 h in O 2. The X-ray powder diffraction (XRD) study show that the crystallinity of SO 4/Zr 1− x Sn x O 2 decreases with the incorporation of Sn. The BET surface areas of SO 4/Zr 1− x Sn x O 2 ( x=0.05–0.35) range from 90 to 124 m 2/g. SO 4/ZrO 2 has a surface area of 87 m 2/g. The surface areas of SO 4/SnO 2 with 2.16 and 2.88 wt.% S are 152 and 101 m 2/g, respectively. The FTIR photoacoustic spectrum of SO 4/ZrO 2 shows Brønsted acid site bands, whereas SO 4/Zr 1− x Sn x O 2 and SO 4/SnO 2 have both Brønsted and Lewis acid site bands. Temperature-programmed desorption of ammonia (NH 3-TPD) results show that acid site distribution are similar for SO 4/Zr 1− x Sn x O 2 ( x=0.05–0.35), but differ from those of SO 4/ZrO 2 and SO 4/SnO 2. Activities of these catalysts were examined for the benzoylation of anisole with benzoyl chloride and benzoic anhydride. The surface acidities and catalytic activities of SO 4/Zr 1− x Sn x O 2 were compared with those of SO 4/ZrO 2 and SO 4/SnO 2.

The role of different nitrogen functional groups on the removal of SO 2 from flue gases by N-doped activated carbon powders and fibres

SO 2 removal from flue gases by carbonaceous materials is determined by their behaviour as catalysts for SO 2 oxidation into SO 3 or H 2SO 4 in the presence of O 2 or O 2 and steam, respectively. Previous studies have demonstrated that nitrogen (N) functional groups are active sites for the adsorption and oxidation of SO 2, although the nature of the N groups with the higher activity had not been established yet. For this reason, in the present work a number of activated carbons (AC) and activated carbon fibres (ACF) doped with N atoms have been prepared using different methods. The number and nature of these N groups have been assessed by XPS. The materials prepared have a wide range of nitrogen content, which is distributed into different chemical species. In this way, we were able to determine the effect of the N content and the role of the different N-containing functional groups on the catalytic activity for SO 2 oxidation. The results confirm that, although the pore volume and the pore size distribution strongly influence the catalytic activity, the presence of N species at the surface increases the catalytic activity. They also demonstrate that, among the different N functional groups, pyridinic nitrogen is the most active for this reaction.

Carbon materials as catalyst supports for SO 2 oxidation: catalytic activity of CuO–AC

Copper catalysts supported on acid treated activated carbon (AC) were prepared, characterized and tested in terms of their SO 2 oxidation activity. Reactions of CuO–AC in flow systems with sulfur dioxide, oxygen and nitrogen streams were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of reaction temperature, acid treatment, metal loading, support particle size, SO 2 concentration and O 2 concentration on SO 2 oxidation activity were evaluated. It was found that carbon materials used as catalyst supports for copper oxide catalysts provided a high catalytic activity for adsorbing SO 2 from flue gas and oxidizing it. Acid pretreatment of the carbon supports increased the content of specific surface chemical groups to enhance the catalytic activity for SO 2 oxidation. Metal loading, as well as support particle size, have a significant influence on the SO 2 activity. The supported metals rather than surface oxygen functional groups on AC may be the active sites for adsorbing SO 2.

Tetragonal structure, anionic vacancies and catalytic activity of SO 42−-ZrO 2 catalysts for n-butane isomerization

An assessment of the influence of the crystal structure, surface hydroxylation state and previous oxidation/reduction pretreatments on the activity of sulfate-zirconia catalysts for isomerization of n-butane was performed using crystalline and amorphous zirconia supports. Different sulfation methods were used for the preparation of bulk and supported SO 4 2−-ZrO 2 with monoclinic, tetragonal and tetragonal+monoclinic structures. Activity was important only for the samples that contained tetragonal crystals. The catalysts prepared from pure monoclinic zirconia showed negligible activity. SO 4 2−-ZrO 2 catalysts prepared by sulfation of crystalline zirconia displayed sites with lower acidity and cracking activity than those sulfated in the amorphous state. Prereduction of the zirconia samples with H 2 was found to greatly increase the catalytic activity, and a maximum rate was found at a reduction temperature of 550–600 °C, coinciding with a TPR peak supposedly associated with the removal of lattice oxygen and the creation of lattice defects. A weaker dependence of catalytic activity on the density or type of surface OH groups on zirconia (before sulfation) was found in this work. A model of active site generation was constructed in order to stress the dependence on the crystal structure and crystal defects. Current and previous results suggest that tetragonal structure in active SO 4 2−-ZrO 2 is a consequence of the stabilization of anionic vacancies in zirconia. Anionic vacancies are in turn supposed to be related to the catalytic activity for n-butane isomerization through the stabilization of electrons from ionized intermediates.

Formation of acid sites in ordered pores of FSM-16 by modification with sulfated zirconia

A mesoporous solid acid with ordered mesopores was prepared by modification of FSM-16 with sulfated zirconia (SO 4 2−/ZrO 2/FSM-16); FSM-16 precalcined at 1123 K was soaked with an ethanol solution of zirconyl chloride, followed by exposing to 0.5 mol dm −3 H 2SO 4 and calcining in air at 873 K. Measurements of XRD and nitrogen adsorption isothermo showed the structure to contain the ordered pores, though its surface area and total pore volume were reduced to 619 m 2 g −1 and 376 cm 3 g −1 compared with 886 m 2 g −1 and 490 cm 3 g −1 for the unmodified FSM-16. The acid sites of zirconia promoted by sulfate ions were formed inside of the ordered pores. The activity of (SO 4 2−/ZrO 2/FSM-16) for 1-butene isomerization was nine times larger than that of the unmodified FSM-16. Two more acid-catalyzed reactions producing relatively large molecules were examined and catalytic activities of SO 4 2−/ZrO 2/FSM-16 were compared with those of sulfated zirconia (SO 4 2−/ZrO 2), which is one of the solid superacids. The activities for Mukaiyama aldol condensation of 1 trimethylsilyloxycyclohexene with benzaldehyde were comparable to each other, but the Friedel–Crafts benzoylation of toluene with benzoyl chloride or benzoic anhydride revealed the present catalyst to be much inferior to the sulfated zirconia for lack of superacidity.

Catalytic activity for synthesis of isomerized products from benzene over platinum-supported sulfated zirconia

The catalytic activity of Pt/SO 4 2−/ZrO 2 in the benzene hydrogenation and isomerization reaction at 250°C is superior to that of other Pt/conventional solid acid catalysts such as Pt/HY-zeolite and Pt/H-mordenite. The catalytic activity of SO 4 2−/ZrO 2 for cyclohexane isomerization to methylcyclopentane at 250°C is higher than that of HY-zeolite and H-mordenite. SO 4 2−/ZrO 2 and HM10 have more Brönsted acid sites of the highest strength and show a higher percentage of isomerization conversion. In contrast, ZrO 2, which contains almost no Brönsted acid sites, and HY5.6, which contains almost no Brönsted acid sites of the highest strength, show a lower conversion percentage. Consequently, Brönsted acid sites of the highest strength are active sites responsible for cyclohexane isomerization. However, the isomerization conversion percentage does not completely correlate with the number of highest-strength Brönsted acid sites, suggesting that not all of these sites contribute to the reaction nor do only Brönsted acid sites influence cyclohexane isomerization. Neither the total number nor the number of highest-strength Lewis acid sites correlates with the isomerization conversion rate, indicating that Lewis acid sites are not responsible for cyclohexane isomerization.

Redox properties and catalytic activity of SO 42−[sbnd]ZrO 2 catalysts for n-butane isomerization Role of transition metal cation promoters

SO 4 2− ZrO 2 catalysts promoted with cations of transition metals (Fe, Cu, Ni, W, Pt, Co, Zn, Cd, Cr) were studied. Their influence on the catalytic activity for the isomerization of n-butane was analyzed in the presence of electron donor (H 2) and electron acceptor (O 2, CO 2) gases. A new reaction scheme accounts for the one electron properties of the sulfate-zirconia catalyst. Transition metal cations are postulated to enhance activity through d-orbital interaction. Cations with a complete d level inhibit activity, but the presence of electron acceptor molecules (O 2 and CO 2) in the reacting medium attenuated this deleterious effect.

Catalytic properties of [formula omitted] superacids in esterification

SO 4 2− Ti-M-O (M = Al, Fe, Sn) solid superacids were used in the esterification of phthalic anhydride with 2-ethyl hexyl alcohol. The catalytic activity of SO 4 2− TiAlSnO (1) is higher than SO 4 2− TiO 2 and SO 4 2− TiAlO solid superacids. In the presence of (1) DOP is prepared in good yield at 175°C over a period of 6 h. The acid strength, surface area and catalytic activity of SO 4 2− Ti-M-O are obviously affected by the preparation conditions. Temperature-programmed desorption of pyridine adsorbed on the catalyst was used to characterize the acid strength distribution of the catalysts. It was found that there were three kinds of acid sites (weak acid, middle acid and superacid) on SO 4 2− TiAlO , and the concentration of the middle-acid site on the catalysts is directly proportional to its catalytic activity for the esterification. Adding Al into SO 4 2− TiO 2 could increase its surface area greatly.