Dehai Xiao

Hydrothermal Method Prepared Ce-P-O Catalyst for the Selective Catalytic Reduction of NO with NH3 in a Broad Temperature Range

Selective catalytic reduction of NOx with ammonia (NH3-SCR) is a widely used process for the abatement of NOx from flue gases and exhaust gases of diesel trucks. The well-known commercial catalysts used for this process are V2O5-WO3/TiO2 or V2O5-MoO3/TiO2 which function within a relatively narrow temperature window of 300–400 8C. As the temperature rises above 400 8C, V-based catalysts exhibit a rapid decrease in activity and selectivity in the reduction of NOx due to the oxidation of SO2 into SO3. [2] Furthermore, the emissions of toxic vanadium lead to health problems. In addition, deactivation by poisoning is another problem because flue gases contain metal oxides (e.g. , K2O) that deactivate V-based catalysts. Therefore, alternative NH3-SCR catalysts with only nontoxic components and stable under harsh operating conditions are required. Low-temperature SCR catalysts, such as amorphous MnOx, [5] Fe–Mn–Ox, [6] MnOx–CeO2, [7] Mn/TiO2, [8] are urgently needed for the abatement of NOx from flue gases to avoid reheating of the gas and thus decrease the capital cost. In the medium temperature range, Fe-based catalysts, such as Fe2O3– WO3/ZrO2, [9] and crystallite iron titanate, exhibit excellent SCR activity. However, these catalysts regularly have problems with low N2 selectivity, H2O and SO2 deactivation, and especially the loss of activity at high temperature and high space velocity. For the high temperature range, some zeolite catalysts, such as Fe-ZSM-5 reported by Long et al. and Carja et al. , have shown highly catalytic performance in the range of 400– 500 8C. However, their applications are greatly restricted by poor hydrothermal stability of the zeolite support. A comprehensive overview of the NH3-SCR reaction mechanism shows that both surface acidity and redox property are necessary for the NH3-SCR reaction. Herein, several metal phosphate catalysts containing different multivalent ions, (M–P–O; M = Cu , Fe + , Mn + , Ce), were prepared. The most promising catalyst, Ce-P-O, is emphasized herein due to its high deNOx activity. The results showed that Ce-P-O(h), prepared by a hydrothermal method (see the Supporting Information), is a novel and efficient catalyst for NH3-SCR with NO conversions above 90 % within the range of 200–550 8C. For comparison, the Ce-P-O catalyst was also prepared by a coprecipitation method and denoted as Ce-P-O(c). Figure 1 shows the comparison of deNOx activities of Ce-P-O catalysts as a function of reaction temperature. Ce-P-O catalysts prepared by hydrothermal and coprecipitation methods exhibited different deNOx performance in low temperatures

A Novel Ce-P-O Catalyst for the Selective Catalytic Reduction of NO with NH3

A novel Ce-P-O catalyst for the selective catalytic reduction of NO with NH3 was synthesized. The Ce-P-O catalyst was calcined at 500 °C and showed higher deNOx activity (NO conversion > 90%) with the temperature range of 300–550 °C and at GHSV = 20 000 h−1. The NO conversion was not significantly affected by the presence of H2O and SO2. By comparison with the commercial V-W-Ti catalyst, the Ce-P-O catalyst exhibited better resistance to deactivation due to K2O poisoning.

CO Oxidation over the Perovskite-Like Oxides La2−xSrxMO4(x= 0.0, 0.5, 1.0; M = Cu, Ni): A Study from Cyclic Voltammetry

Abstract Correlations between the catalytic performance and the electrochemical properties in heterogeneous catalysis were observed, using perovskite-like oxides La2−xSrxMO4 (x = 0.0, 0.5, 1.0, M = Cu, Ni) as the model catalysts and CO oxidation as the probe reaction. For a reaction that contains reducing agent in the feed gas, the activity depends mainly on the area of redox peak in the CV curves, while has no much relation to the symmetry of the redox potentials. The irreversible cycle in the first CV curves of LaSrCuO4 suggested that the first step of the reaction is adsorption, corresponding to Mn+ (Cu2+) to M(n+1)+ (Cu3+).

Silanized Titanium Silicate (TS-1) Molecular Sieve for Promoting the Homogeneously Catalyzed Oxidation of Cyclohexane

Abstract The promoting effect of titanium silicate (TS-1) molecular sieve and silanized TS-1 (TS-1-S) on the homogeneous liquid oxidation of cyclohexane catalyzed by cobalt naphthenate (Co-nap) with oxygen as oxidant was investigated. Both TS-1 zeolites were efficient promoters. The conversion of cyclohexane was 7.9% with a selectivity of 83.7% when it was catalyzed by Co-nap/TS-1-S, and the reaction time was reduced to 130 min as compared to 300 min with Co-nap as the catalyst. The adsorption of Co-nap on TS-1-S, which transformed a homogeneous reaction into a “quasi-heterogeneous” reaction, was the reason for the better catalytic performance.

Aerobic oxidation of benzyl alcohol by Fe-system catalyst

Abstract The catalytic oxidation of benzyl alcohol has been carried out by using dioxygen as oxidant in the presence of Fe(acac)3 (acetyl acetone)/1,10-phenanthroline/base system in toluene at 80°. Oxygen was activated successfully by the Fe-catalyst and oxidized benzyl alcohol to benzyl aldehyde in ∼100% selectivity. It was found that the oxidation of benzyl alcohol was very sensitive to water in this reaction system, and small amount of water could obviously decrease the reactivity. Based on the results of cyclic voltammetry and ESR, a binuclear-Fe mechanism was also proposed.

Excellent performance of La1-xCexSrNiO4 (x ≤ 0.3) for no decomposition in the presence of excess oxygen

Abstract Ce involved perovskite-like oxides (La1−xCexSrNiO4, x ≤ 0.3) show high activity for NO decomposition even in the presence of excess oxygen, which might be mainly ascribed to the new active site formed in the catalyst due to the entry of Ce to the La site of LaSrNiO4.

Effect of the Addition of In to Co/HMCM-49 Catalyst for the Selective Catalytic Reduction of NO Under Lean-burn Conditions

Abstract Selective catalytic reduction (SCR) of NO with propane using bimetals (3Co2Ce, 3Co2Sr, 3Co2Sn and 3Co2In) loaded on HMCM-49 zeolite was studied under lean-burn condition. Only 3Co2In/HMCM-49 exhibited higher deNOx activity in a wide temperature range. The catalysts were characterized by N2-adsoption, X-ray diffraction (XRD), temperature-programmed surface reactions (TPSR) and temperature-programmed desorption (TPD) of NO. TPSR and TPD results exhibited that the addition of In inhibited the oxidation ability of Co on 3Co2In/HMCM-49 catalyst, but enhanced NOx adsorption.

Mechanism of NO decomposition on perovskite (-like) catalysts

NOx emitting from industrial and mobile exhaust are serious pollutant in air atmosphere, and the removal of them is an urgent task of today in environment-protection field. Although the present three-way-catalyst (TWC) can remove NOx from the mobile exhaust effectively, it will be out of work as lean-burn strategies are used to increase energy efficiency (for example, the diesel engine operated in the lean-burn condition), hence, the technology that can remove NOx in the presence of excess oxygen is desired. In addition, because the capability of noblemetal catalyst for NOx removal is weak at high temperatures (>873 K), it is thus necessary to comprehend the process of NOx decomposition, which would help to solve the problem of NOx removal. For NO decomposition reaction (2NO = N2 + O2), it is generally accepted that N2 was formed through the decomposition of N2O species, i.e. 2NO N2O + Oads and N2Oads N2 + Oads . While the way of oxygen formation is still unclear at present. According to the literatures, there are two proposed ways for oxygen desorption, that is, i) the direct desorption of two vicinal oxygen, Oads + Oads O2; and ii) the indirect desorption with NO as an intermediate, NOads + Oads NO2, NO2 + Oads NO3 ads, NO3 ads NO + O2. Accordingly, there are two ways for NO2 formation, that is, iii) reaction of gaseous NO and O2 occurring in the downstream, O2 + 2NO 2NO2; and iv) reaction of adsorbed O atom and NO occurring on the catalyst surface, Oads + NOads NO2. Recently, Iglesia et al. suggested that the O2 formation over Cu-ZSM-5 mainly occurred through the decomposition of NO3(a) species, but there is still no literature discussing the way of O2 and NO2 formation over perovskite (-like) oxides. In this work, by discussing the possible reaction steps occurring in the process of NO decomposition, we proposed that the way of NO decomposition over perovskite (-like) mixed oxides occurred with NO2 as an intermediate, and NO2 was mainly formed on the catalyst surface in the way of Oads + NOads NO2, while O2 was formed through the dissociation of NO2 species in the way of 2NO2(g) = 2NO(g) + O2(g). The samples, LaSrNiO4 and La0.4Sr0.6Mn0.8Ni0.2O3, were prepared by the conventional citric combustion method. O2-TPD experiment was carried out on a homemade apparatus equipped with a thermal conductivity detector (TCD). The samples (0.2 g) were first treated in O2 at 1073 K for 1 h and cooled to room temperature in the same atmosphere, then swept with pure He (or 0.5% O2/He) at a rate of 11.8 mL/min until the base line on the recorder remained unchanged. Finally, the sample was heated at a rate of 20 K/min in He (or 0.5% O2/He) to record the TPD profile. Steady-state activities of catalysts were evaluated using a single-pass flow micro-reactor made of quartz, with an internal diameter of 6 mm. The reactant gas (1% NO/He + 0% 10% O2/He) was passed through 0.5 g (in the absence of oxygen) or 1.0 g (in the presence of oxygen) catalysts at a rate of 25 or 40 mL/min (in all, to keep W/F = 1.2 g·s·cm ). The gas composition was analyzed before and after the reaction by an on-line gas chromatography, using molecular sieve 5A column for separating NO, N2 and O2. N2O was not analyzed here because it was difficult to form between 773 and 1123 K as reported in ref. [9]. Before the data were obtained, reactions were maintained for a period of ~2 h at each temperature to ensure the steady-state conditions. According to the literatures reported previously, the possible reaction steps occurring in the process of NO decomposition are summarized in Table 1.

A method for quantitative analysis of nitrogen oxides and N2 by means of mass spectrometry with the assistance of a catalytic technique for the reduction of NO with CO or hydrocarbons

Mass spectrometry is not able to differentiate NO x and N2 from other interferences (e.g. CO and C2H4) in the deNO x reactions. In the present study, a quantitative method for analysis of NO x and N2 simultaneously in these reactions with an assisted converter operated at higher temperature under O2-rich condition, which eliminates the interferences, is developed. The NO x conversion from this method is comparable to the one from an Automotive Emission Analyser equipped with NO x electrochemical sensor. Two types of deNO x reactions are tested in terms of selectivity of N2 production. The application of this method is discussed.