Effects of support acidity on the reaction mechanisms of selective catalytic reduction of NO by CH_(4) in excess oxygen

The reaction mechanisms of selective catalytic reduction(SCR)of nitric oxide(NO)by methane(CH4)over solid superacid-based catalysts were proposed and testified by DRIFTS studies on transient reaction as well as by kinetic models.Catalysts derived from different supports would lead to different reaction pathways,and the acidity of solid superacid played an important role in determining the reaction mechanisms and the catalytic activities.Higher ratios of BrØnsted acid sites to Lewis acid sites would lead to stronger oxidation of methane and then could facilitate the step of methane activation.Strong BrØnsted acid sites would not necessarily lead to better catalytic performance,however,since the active surface NO_(y) species and the corresponding reaction routes were determined by the overall acidity strength of the support.The reaction routes where NO_(2)moiety was engaged as an important intermediate involved moderate oxidation of methane,the rate of which could determine the overall activity.The reaction involving NO moiety was likely to be determined by the step of reduction of NO.Therefore,to enhance the SCR activity of solid superacid catalysts,reactions between appropriate couples of active NO_(y)species and activated hydrocarbon intermediates should be realized by modification of the support acidity.

POLYMER-SUPPORTED LEWIS ACID CATALYSTS. Ⅵ. POLYSTYRENE-BONDED STANNIC CHLORIDE CATALYST

A polystyrene-bonded stannic chloride catalyst was synthesized by the method of lithium polystyryl combined with stannic chloride. This catalyst is a polymeric organometallic compound containing 0.25 mmol Sn (Ⅳ)/g catalyst. The catalyst showed sufficient stability and catalytic activity in organic reaction such as esterification, acetalation and ketal formation, and it could be reused many times without losing its catalytic activity.

Synthesis of Poly(styrene-co-divinylbenzene)-supported Dichloro Cyanuric Acid

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Vapor-phase Nitration of Benzene to Nitrobenzene over Supported Sulfuric Acid Catalyst

Vapor-phase nitration of benzene over solid acid catalyst is expected to be a clean process with no sulfuric acid waste. We investigated this process over solid acidic catalysts utilizing diluted nitric acid (60-70%) as nitrating agent, and found that supported sulfuric acid catalyst exhibited a very high catalytic activity. Under the conditions of reaction temperature 160-170℃, space velocity (SV) 1200 h-1, the yield and the space-time yield (STY) of nitrobenzene (NB) based on HNO3 were more than 98% and 0.75 kg穔gcat-1穐-1 over 10% H2SO4/SiO2 (by weight) catalyst respectively.

Alkylation of Hydroquinone with tert-Butyl Alcohol over Bis[（perfluoroalkyl）sulfonyl]imides Supported on MCM-41

Bis[（perfluoroalkyl）sulfonyl]imides [HN（SO2Rf）2, and Rf represents the perfluorinated alkyl group] supported on MCM-41 were synthesized and characterized by XRD, FTIR, SEM, TGA and N2-adsorption techniques. The supported catalysts, HN（SO2Rf）2/MCM-41, were used as the catalysts for the tert-butylafion of hydroquinone （HQ） with tert-butyl alcohol （TBA） in the liquid phase. A high yield （52.0%） of 2-tert-butyl hydroquinone （TBHQ） could be obtained in the presence of 5 tool% HN（SO2C4F9）2/MCM-41 under the optimized reaction conditions and the heterogeneous catalyst could be recycled at least 6 times without substantial loss of activity.

Effects of support property on the catalytic performance of CeO_2-ZrO_2-CrO_x for 1,2-dichloroethane oxidation

HZSM-5, Al_2O_3, TiO_2 and SiO_2 supported CeO_2-ZrO_2-CrO_x catalysts were prepared by deposition-precipitation method and tested for deep catalytic oxidation of 1,2-dichloroethane（DCE）, as one of the common chlorinated organic pollutants. All the catalysts were characterized by means of N_2 adsorption-desorption, X-ray photoelectron spectroscopy（XPS）, ammonia-temperatureprogrammed desorption（NH_3-TPD） and hydrogen temperature-programmed reduction（H2-TPR）. The characterization results revealed that there was strongly synergistic effect between the oxidizability of CZCr species and the acidity of supports, which obviously promoted the catalytic activity for DCE degradation. 20% CZCr/HZSM-5 showed the highest activity and good durability during the long-term continuous test. The catalytic activity decreased in the order： 20%CZCr/HZSM-5〉CZCr〉20%CZCr/TiO_2〉20%CZCr/Al_2O_3〉20%CZCr/SiO_2.

Effects of tungsten oxide on the activity and thermal stability of a sulfate-derived titania supported platinum catalyst for propane oxidation

A Pt/WO3/TiO2 catalyst for propane oxidation was prepared by a stepwise wet impregnation method, and was aged at 800°C for 5 hr. Compared to the sulfate-derived titania supported catalyst, the introduction of tungsten oxide as stable Br nsted acid sites led to the formation of more metallic platinum active sites at the Pt/WO3 interface. The dissociation of surface intermediates for propane oxidation was promoted on the WO3-modified catalyst. This, as well as the inhibition effects of tungsten oxide on the sintering of anatase and the phase transformation to rutile, resulting in a high activity and thermal stability for the Pt/WO3/TiO2 catalyst.

Silica Supported Perchloric Acid： A Convenient and Environmentally Friendly Catalyst for the One-pot Multicomponent Synthesis of ,β-Acetamido Ketones

A modified Dakin-West one-pot, four-component condensation of an aryl aldehyde, aryl ketone, acetyl chloride and acetonitrile in the presence of silica supported perchloric acid as an active, inexpensive, recoverable and recyclable catalyst is reported for the synthesis of β-acetamido ketones under mechanical stirring and ultrasonic irradiation conditions. This system has advantages of short reaction times, good to excellent yields and the ability to carry out the large scale reactions. The use of ultrasound increases the rate of reactions compared with reactions at reflux conditions.

Application of silica-alumina as hydrothermally stable supports for Pt catalysts for acid-assisted soot oxidation

In this work,silica-alumina mixed oxides with different SiO_(2)contents(5%and 30%)were adopted as acidic supports for platinum catalysts for soot oxidation.The obtained catalysts were hydrothermally aged in 10%H_(2)0/air at 750℃for 20 h.The catalysts were characterized by X-ray diffraction(XRD),N_(2)adsorption,inductively coupled plasma(ICP),CO chemisorption,NH3temperature-programmed desorption(TPD),infrared(IR)spectroscopy of CO adsorption,temperature-programmed oxidation(TPO)of NO,and TPD of NO_(x).The surface acidity of catalyst was positive correlated with the content of SiO_(2),which kept platinum in metallic and partially oxidized states in an oxidizing atmosphere.Compared with sulfation treatment on the alumina support,the application of SiO_(2)-Al_(2)O_(3)mixed oxides does not result in the coverage of Pt active sites and the prepared catalysts exhibit excellent activity for NO oxidation.They promote NOxpreferential adsorption on soot and decomposition of surface oxygenated compounds(SOCs)as the sulfated Pt/Al_(2)O_(3)catalyst does.

Silica-supported Perchloric Acid Catalyzed One-pot Synthesis of 1,4-Dihydropyridines

An environmentally friendly and highly efficient procedure for the preparation of 1,4-dihydropyridines by the reaction between a,β-unsaturated aldehydes, aromatic amines and β-keto esters in the presence of silica supported perchloric acid is described.

Silica Supported Methanesulfonic Acid as an Efficient and Reusable Heterogeneous Catalyst for the Synthesis of Amidoalkyl Naphthols

A green protocol for the preparation of amidoalkyl naphthols from three-component one-pot condensation of 2-naphthol, aldehydes, amides or urea in the presence of silica supported methanesulfonic acid under thermal sol- vent-free conditions has been described. The catalyst is stable, efficient, easily prepared, and reusable. The remarkable features of this methodology are short reaction time, excellent yields, simple experimental and work-up procedures.

The contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using diamond anodes

In this work, the contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using boron-doped diamond（BDD） anodes was investigated in different electrolytes. A complete mineralization of cyanuric acid was obtained in Na Cl;however lower degrees of mineralization of 70% and 40% were obtained in Na2SO4 and Na Cl O4, respectively. This can be explained by the nature of the oxidants electrogenerated in each electrolyte. It is clear that the contribution of active chlorine（Cl2, HCl O, Cl O-）electrogenerated from oxidation of chlorides on BDD is much more important in the electrolytic degradation of cyanuric acid than the persulfate and hydroxyl radicals produced by electro-oxidation of sulfate and water on BDD anodes. This could be explained by the high affinity of active chlorine towards nitrogen compounds. No organic intermediates were detected during the electrolytic degradation of cyanuric acid in any the electrolytes, which can be explained by their immediate depletion by hydroxyl radicals produced on the BDD surface. Nitrates and ammonium were the final products of electrolytic degradation of cyanuric acid on BDD anodes in all electrolytes. In addition, small amounts of chloramines were formed in the chloride medium. Low current density（≤ 10 m A/cm2） and neutral medium（p H in the range 6–9） should be used for high efficiency electrolytic degradation and negligible formation of hazardous chlorate and perchlorate.