Selective Catalytic Reaction Research Articles

Effects of Preparation Methods on the Catalytic Performance of Selective Catalytic Reduction of NO with CH<sub>4</sub> over Co-MOR Catalysts

A series of Co-mordenite (MOR) catalysts prepared by ion-exchange or impregnation methods were used in the selective catalytic reaction of NO with methane (CH 4 -SCR). The structure and physicochemical properties of the catalysts were examined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), UV-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of NO (NO-TPD). The Co species in the catalyst prepared by impregnation is present as Co 3 O 4 , whereas in the catalyst prepared by an ion-exchange method, the Co species enter in the mordenite skeleton with the ion form, and the more Co 2+ and [Co-O-Co] 2+ formed in the catalysts, the more uniform the adsorption of NO centers and the active centers of CH 4 -SCR. The catalysts prepared by different methods exhibited different activities for CH 4 -SCR. The catalysts prepared by ion-exchange exhibited activity over a wide activity temperature region, and NO conversion was over 50% at 327-450 °C on the Co(0.30)-MOR catalyst.

Enhancement of Catalytic Activity Over the Iron-Modified Ce/TiO2 Catalyst for Selective Catalytic Reduction of NOx with Ammonia

A series of iron-modified Ce/TiO2 catalysts with different Fe/Ti molar ratios were prepared by an impregnation method and used for selective catalytic reaction (SCR) of NOx with NH3. The Fe–Ce/TiO2 catalyst with a Fe/Ti molar ratio of 0.2 had good low-temperature activity and sulfur-poisoning resistance compared with the Ce/TiO2 catalyst. The introduction of Fe could increase the amount of Ce3+ and chemisorbed oxygen species on the catalyst surface and thereafter generate more ionic NH4+ and in situ formed NO2, respectively. In addition, the dispersion of cerium oxide could be improved by the addition of iron, and no visible phase of iron oxide could be observed at low Fe/Ti molar ratios (≤0.2). All of these factors played significant roles in the enhanced catalytic activity, especially the low-temperature activity. Furthermore, mechanisms of the SCR reaction and the SO2 poisoning of the Fe(0.2)–Ce/TiO2 catalyst were studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. Coordi...

SCR 공정에서 Calcium 성분이 V2O5/TiO2촉매 활성에 미치는 영향

장기간 운전되는 선택적 촉매 반응공정(SCR Process)에서 <TEX>$V_2O_5/TiO_2$</TEX> 촉매의 활성저하에 미치는 요소들에 대해 고찰하였다. <TEX>$V_2O_5/TiO_2$</TEX> 촉매의 활성은 공정이 8개월 정도 운전되었을 때 급격히 감소하였다. ICP-AES 분석결과, 공정에서 사용된 <TEX>$V_2O_5/TiO_2$</TEX> 촉매의 활성이 저하되는 것은 선택적 촉매반응공정에서 환원제로 요소용액에 첨가된 칼슘성분에 기인되는 것으로 사료되었다. <TEX>$NH_3$</TEX>-TPD 실험결과, 칼슘성분과 같은 강한 염기성 성분은 촉매의 산도에 매우 큰 영향을 미치는 것으로 나타났다. 이와 같은 결과로 비록 농도가 매우 적은 범위라도 칼슘성분이 선택적 촉매 반응공정에서 촉매의 활성도 저하의 원인이 되는 것으로 사료되었다. Factors acting on the deactivation of <TEX>$V_2O_5/TiO_2$</TEX> catalysts were investigated in the selective catalytic reduction(SCR) process for long term operation. The activity of <TEX>$V_2O_5/TiO_2$</TEX> catalysts was decreased rapidly after 8 months from the starting of operation in the selective catalytic reaction processes. From ICP-AES analysis, the deactivation of the used catalysts could be caused from the calcium component included in urea solution as a reducing agent. It was found from the <TEX>$NH_3$</TEX>-TPD experiments that the strong basic element like Ca component drastically affected the acidity of the <TEX>$V_2O_5/TiO_2$</TEX> catalyst. The results gave an explanation on the reason why the component of Ca, even though its concentration is very low, could lead to the deactivation of <TEX>$V_2O_5/TiO_2$</TEX> catalyst in the selective catalytic reaction processes.

WO3 Modification of MnOx/TiO2 Catalysts for Low Temperature Selective Catalytic Reduction of NO with Ammonia

A series of WO 3 -modified MnO x /TiO 2 catalysts were prepared by three different impregnation methods and were investigated by specific surface area measurement, X-ray diffraction, laser Raman spectroscopy, H 2 temperature-programmed reduction, high-resolution transmission electron microscopy, and in situ Fourier transform infrared spectroscopy. The three-component catalysts obtained with the one-step impregnation exhibited the best catalytic activity. The characterization data revealed that a synergism between tungsten and manganese oxide existed in the catalysts when tungsten was loaded either prior to or simultaneously with manganese, which made the active components better dispersed and blocked the transformation of TiO 2 from the anatase to rutile structure. The manganese oxide existed in the form of Mn 2 O 3 on all the samples but was accompanied by a small amount of MnO 2 for 15%MnO x −5%WO 3 /TiO 2 . WO 3 improved the reducibility and enhanced the amount and strength of the surface acid sites, especially the Brönsted acid sites and promoted the formation of the active intermediate ((NH 2 ). Lewis acid sites had the major role in the low temperature selective catalytic reduction reaction while surface (NH 2 was an important intermediate species. 采用 3 种不同的浸渍过程制备了系列 WO 3 改性 MnO x /TiO 2 催化剂, 并采用 BET 比表面积测试 X 射线衍射 拉曼光谱 H 2 程序升温还原 高分辨扫描电镜和原位红外光谱等技术进行表征. 结果显示, 一步浸渍法和先钨后锰的分布浸渍法制备的催化剂中, Mn 和 W 的协同作用提高了活性组分的分散状态, 并阻止了钛载体的转晶; 在所有的 Mn 基催化剂中, Mn 物种主要以 Mn 2 O 3 形式存在, 但在 15%MnO x -5%WO 3 /TiO 2 中出现了少量的 MnO 2 ; WO 3 的加入大大增强了催化剂的还原能力, 提高了其表面酸位尤其是 B 酸的数量与强度, 并促进了活性中间物 (-NH 2 ) 的生成. 表面 Lewis 酸在低温 SCR 反应起主要作用, 并且发现-NH 2 也是活性很高的物种. 在 NH 3 低温催化还原 NO 的反应中, 一步浸渍法制备的催化剂活性最高. WO 3 addition improved the reducibility and enhanced the amount and strength of the surface acid sites of a Mn-based catalyst synthesized by a one-step impregnation method, and it showed excellent activity.

ChemInform Abstract: The Past, Present and Future of Heterogeneous Catalysis

AbstractReview: 459 refs.

Size-Dependent Catalytic Performance of CuO on γ-Al2O3: NO Reduction versus NH3 Oxidation

Catalytic reaction pathways of NH3 on CuO/γ-Al2O3 catalysts during NH3 selective catalytic reduction reactions were investigated under oxygen-rich conditions. On 10 wt % CuO/γ-Al2O3, NH3 reacted with oxygen to produce NOx. In contrast, on the 0.5 wt % CuO/γ-Al2O3 catalyst, NH3 reacted primarily with NO to form N2 with a conversion efficiency of ∼80% at 450 °C. H2-temperature-programmed reduction (H2-TPR) results show that Cu species present in 10 wt % CuO/γ-Al2O3 can be easily reduced at ∼160 °C, which suggests the formation of large CuO clusters on the alumina surface. On the other hand, the TPR spectrum obtained from the 0.5 wt % CuO/γ-Al2O3 catalyst does not show any measurable H2 consumption up to 700 °C, which suggests the presence of nonreducible isolated Cu species in this catalyst. Scanning transmission electron microscopy images collected from 10 wt % CuO/γ-Al2O3 show nanosized CuO clusters, but no evidence of cluster formation is seen in the images recorded from the 0.5 wt % CuO/γ-Al2O3 sample d...

The past, present and future of heterogeneous catalysis

This review highlights key catalytic discoveries and the main industrial catalytic processes over the last 300 years that involved commodities, fine chemicals, petrochemicals, petroleum transformation for fuels and energy supply, emission control, and so forth. In the past, discoveries have often followed events such as wars or embargos, whereas the current driving forces of studies, researches and then discoveries aim at a better understanding of catalytic processes, at reducing the costs of raw materials and processes, at developing new catalytic materials and at addressing environmental issues. This review focuses on the history of many catalytic industrial processes, environmental issues, catalytic materials, especially their expected catalytic properties, on catalyst characterisation by physical methods and development of in situ conditions, i.e., characterisation under actual working conditions with reactants and products analyzed on-line. Emphasis is also placed on high selectivity in catalytic reactions and the major challenges for the future, such as environmental issues, energy supply, pollution control for vehicles and industrial plants, air/VOCs/water purification, hydrogen sources and carbon dioxide storage/up grading, transformation of biomass as a promising source of raw materials, and catalytic water splitting perspectives.This review is a survey of heterogeneous catalysis and is not comprehensive but leads to the conclusion that, although many catalysts and catalytic processes have already been discovered and developed over the past century, many opportunities nevertheless exist for new developments, new processes and new catalytic materials. It follows that substantial challenges exist for the younger generation of researchers and engineers, as emphasized at the end of the manuscript.

An investigation into the properties of V-based catalysts for Selective Catalytic Reduction of NO with NH3

Selective catalytic reduction (SCR) is the most potential method for removing marine NOx emissions by up to 95%. This paper presents the results of an investigation using vanadium (V) based catalysts doped by metals W (tungsten), Ce (cerium) and Ni (nickel) to improve the low temperature performance of an SCR for NOx reduction. The temperature range studied was between 100–450°C with intervals of 100°C. A honeycomb ceramic substrate was modified by composite sol and coated with the catalysts. The study also included preparation, characterisation and activity tests of the selected catalysts, including studying the activity of the catalysts in ammonia selective catalytic reduction reaction with an excess of oxygen concentration.The investigation verifies that a mixture of the above metallic catalysts exhibit high activity for selective catalytic reduction of NOx with ammonia. Among all the catalysts studied, the mixed catalyst of Ni-Ce-W-V is the most potential one, not only because of its higher NOx conversion rate at low temperature, but also because of its wider window of operation temperature.

Adsorption of NO and NH3 over CuO/γ-Al2O3 catalyst

The selective catalytic reduction reaction belongs to the gas-solid multiphase reaction, and the adsorption of NH3 and NO on CuO/γ-Al2O3 catalysts plays an important role in the reaction. Performance of the CuO/γ-Al2O3 catalysts was explored in a fixed bed adsorption system. The catalysts maintain nearly 100% NO conversion efficiency at 350 °C. Comprehensive tests were carried out to study the adsorption behavior of NH3 and NO over the catalysts. The desorption experiments prove that NH3 and NO are adsorbed on CuO/γ-Al2O3 catalysts. The adsorption behaviors of NH3 and NO were also studied with the in-situ diffusion reflectance infrared Fourier transform spectroscopy methods. The results show that NH3 could be strongly adsorbed on the catalysts, resulting in coordinated NH3 and NH 4 + NO adsorption leads to the formation of bridging bidentate nitrate, chelating bidentate nitrate, and chelating nitro. The interaction of NH3 and NO molecules with the Cu2+ present on the CuAl2O4 (100) surface was investigated by using a periodic density functional theory. The results show that the adsorption of all the molecules on the Cu2+ site is energetically favorable, whereas NO bound is stronger than that of NH3 with the adsorption site, and key information about the structural and energetic properties was also addressed.

Modeling and Simulation of Selective Catalytic Reduction for Flue Gas Denitration in Power Plants

Based on Eley-Rideal kinetic mechanism, one dimensional mathematical model for selective catalytic reduction reaction was established, in order to simulate the SCR process in the catalyst channel. The thermal effect on the reaction and the side effect of ammonia oxidation in the channel were considered simultaneously in the modeling. The model was testified to be reliable by compared with the experimental data. By the model, the concentration and temperature distributions in the channel were simulated. The effects of catalyst structure parameters, such as the pitch, the shape of catalyst channel and the monolithic catalyst type, on de-NOX efficiency were studied emphatically. The simulation results would be as an important reference for the design of SCR catalyst in the practical application.

Study of n-C12H26 reforming over DFC catalyst in a simulated diesel exhaust

In lean-DeNOX catalysis reactions, hydrogen is a good reducing agent in PGM catalysts as well as an effective promoter in selective catalytic reduction reactions over base metal oxide catalysts. However, such a lean-DeNOX system, which uses hydrogen, requires an on-board fuel reforming system applicable to internal combustion engines. In this study, catalytic partial oxidation (CPOx) performance was tested in a laboratory for various reactants and hydrocarbon conditions. Volume concentrations of 5–10% oxygen and 0-5% water vapor were used to simulate diesel exhaust, and n-C12H26 was used as the feedstock for the reforming reaction. In the CPOx of n-C12H26, the highest hydrogen selectivity was 64% and was achieved at 100,000 h-1 GHSV. Additionally, the C/O ratio was less than unity in the absence of water vapor. However, as the water concentration was increased to 2.5 and 5.0 vol. % in the n-C12H26 CPOx reactions, the maximum hydrogen selectivity was increased from 64% in the absence of water to 70% and 75%, respectively. This effect is a consequence of the water-gas shift reaction over the catalyst bed. Regarding oxygen concentration effects, hydrogen selectivity slightly increased with increasing oxygen concentration from 10% to 15%. It was also found that the CPOx reaction of n-C12H26 can be ignited at temperatures below 300 C. Accordingly, it can be concluded that CPOx is a useful and feasible device for promoting diesel DeNOx catalysis in terms of hydrogen productivity and reaction initiation.

Oxidation, reemission and mass distribution of mercury in bituminous coal-fired power plants with SCR, CS-ESP and wet FGD

Mercury (Hg) speciation variations in flue gas at the inlet and outlet of various air pollution control devices (APCDs) were studied, including a selective catalytic reactor (SCR), a cold side-electrostatic precipitator (CS-ESP), a wet flue gas desulfurization system (wet FGD) and the stack of bituminous coal-fired power plants. Effects of flue gas temperature, flow rate and selected flue gas components on Hg oxidation were also studied. The association of selected parameters on Hg0 oxidation and removal by the APCDs and the mass distribution of Hg within the system were estimated. Sampling and analysis were carried out using the Ontario Hydro Method. Solid and liquid samples were analyzed according to US EPA methods 7470A and 7471A, respectively. Hg concentration in the flue gas at the outlet boiler and stack ranged from 4.70 to 27.3μg/Sm3 and 3.1 to 0.48μg/Sm3, respectively. The overall Hg removal efficiency in the APCDs ranged from 43.8% to 94.9%, and oxidized Hg in flue gas decreased with increasing temperature. With an increase in HCl concentration, a decrease in flue gas flow rate and decreasing temperature, oxidation of elemental Hg in combustion flue gas increased. The effects of SOx and NOx concentrations on elemental Hg oxidation in flue gas were rather complex. Among the parameters studied, the most significant parameters affecting overall Hg removal in the APCDs, in order, were removal in the ESP, oxidation in the SCR system and removal in the wet FGD. Experimental data and statistical analysis confirmed the promotion of a co-beneficial control of Hg in the SCR, CS-ESP and wet FGD configurations. The mass distribution showed that 43.0% of Hg was collected in ESP fly ash, 49.4% in wet FGD by-products and effluents, 3.9% of Hg was removed in boiler bottom ash and 3.7% was released into the atmosphere. In the SCR+CS-ESP+wet FGD configuration, a major portion of Hg was distributed into the by-products and removed by the APCDs compared to the lower removal levels seen in the CS-ESP+wet FGD configuration.

Modelling of the Selective Catalytic NOx Reduction for Diesel Engine

As Future emission limits of diesel engines is more stringent, model-based control strategy of selective catalytic reduction (SCR) is becoming necessary. Therefore, a catalytic converter mathematical model for simulating selective catalytic deNOx reaction is very important. In this paper, a one dimension catalytic converter mathematical model that consists of thermal energy model, SCR reaction model and NH3storage model for simulating urea-SCR reaction process is presented. Based on this model, the impact of temperature and gas hourly space velocity (GHSV) on NOx conversion efficiency has been researched. According to the results of simulation, it shows good agreement with experimental data.

Fluidized bed plasma for pre-treatment of Co-ferrierite catalysts: An approach to NO x abatement

Replacement of calcination procedures used during catalyst preparation, by a plasma treatment, was studied over a Co-ferrierite (Co-FER) catalyst. The catalyst was tested in the NO x selective catalytic reduction reaction. A combination of UV–Vis spectroscopy and TG analysis revealed the presence of ammonium ions on the untreated and plasma Co-FER samples but not on the calcined one. Therefore, it can be concluded that the plasma treatment was not able to replace the thermal calcination step. The evaluation of catalyst behaviour was performed both under temperature programmed surface reaction (TPSR) and under steady-state conditions at different temperatures. NO oxidation tests showed that, during TPSR runs, calcined catalyst produces more NO 2 than plasma catalyst. NO x consumption during TPSR of plasma catalyst confirms that precursors used on the ion-exchange procedure are still present on the catalyst even after the plasma treatment, reacting with NO to produce R-NO x , N 2O and N 2. Concerning deNO x tests using ethanol as reducing agent, TPSR tests showed higher NO x conversions over untreated and plasma catalysts due to the presence of ammonium and acetate precursors on these catalysts. Untreated, plasma and calcined catalysts present the same NO x and CO x conversions in isothermal tests.

Methane activation and partial oxidation on free gold and palladium clusters: Mechanistic insights into cooperative and highly selective cluster catalysis

The catalytic activation, dehydrogenation, and direct oxidative conversion of methane into more valuable products such as larger hydrocarbons, alcohols, aldehydes etc. are of considerable industrial interest. To investigate the energetics and kinetics of elementary bond-breaking and bond-formation processes, free metal clusters can serve as versatile catalytic model systems. In this context, temperature dependent reactions of small cationic gold clusters Au(x)+ with methane as well as a mixture of methane and molecular oxygen have been performed in an octopole ion trap under multi-collision conditions and compared with the corresponding reactions on palladium clusters Pd(x)+ (x = 2-4). Binding energies of methane to all investigated cluster cations are determined from kinetic measurements via statistical analysis. Furthermore, among the gold clusters, the dimer Au2+ is found to be able to dehydrogenate methane and to convert it into ethylene in a highly selective catalytic reaction. In contrast, all investigated palladium clusters activate methane under non-selective formation of a variety of dehydrogenated products. Most interestingly, methane dehydrogenation is observed for Pd(x)+ and Au2+ only, if a cluster specific 'critical number' of methane molecules is pre-adsorbed. This emphasizes the importance of cooperative coadsorption effects in the dehydrogenation process on these clusters. Finally, the reaction between Au2+ and both O2 and CH4 yields a low temperature product of the stoichiometry Au2(C3H8O2)+ that clearly contains activated O2 and dehydrogenated methane indicating a possible C-O bond formation process. The palladium dimer Pd2+ on the other hand exhibits only the mere coadsorption of molecular oxygen and non-dehydrogenated methane.

Dispersion of Barium Titanate and Strontium Titanate Nanocubes and their Selective Accumulations

Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

Dynamic Methods in Catalytic Reaction Engineering: Applications to the Investigation of the NH3 Selective Catalytic Reduction Reactions for Diesel Emission Control

For the case of the NH3 selective catalytic reduction (NH3-SCR) reactions over V-based and metal-exchanged zeolite catalysts, we have used step response and temperature-programmed experiments in a fixed-bed flow microreactor in order to accomplish the following. (i) Identify the adspecies and evaluate their storage capacities: it was found that, in addition to ammonia, NO2 as well is adsorbed in comparable amounts onto SCR catalysts in the form of nitrites and nitrates. (ii) Investigate the individual steps of mechanistic schemes: the key role of surface nitrates in the NO2-related SCR chemistry was demonstrated by dedicated transient experiments. (iii) Discriminate rival mechanistic hypotheses: the differences in the temporal evolutions of NO and NO2 during transient runs unambiguously indicated that they participate in different steps of the fast SCR mechanism. (iv) Analyze the red-ox features of the catalytic mechanism: specifically designed transient tests highlighted the superior efficiency of surface nitrates in reoxidizing the V-related redox sites. (v) Evaluate surface kinetics: chemically consistent transient kinetic models were developed from systematic sets of transient runs and applied to design and optimization of commercial SCR converters for vehicles. The results of the overall SCR investigation prove that transient response techniques can yield a superior level of mechanistic and kinetic information under process relevant conditions with a limited experimental effort.

Ascertaining p,p′-Dimercaptoazobenzene Produced from p-Aminothiophenol by Selective Catalytic Coupling Reaction on Silver Nanoparticles

Combining experiment and theory, evidence from surface-enhanced Raman scattering (SERS) were obtained for p,p'-dimercaptoazobenzene (DMAB) produced from p-aminothiophenol (PATP) by selective catalytic coupling reaction on silver nanoparticles. The time-dependent SERS spectra of PATP are consistent with the calculated SERS spectra of DMAB, which is the direct evidence for the production of DMAB from PATP by selective catalytic coupling reaction on silver nanoparticles. The so-called "b(2) modes" of PATP is the -N=N- related vibrational modes of DMAB. The silver nanoparticles could be assembled together to form different size of aggregates with different concentration of PATP solution. When the concentration of Ag nanoparticle (the radius 40 nm) in colloid is 35 pM, the time-dependent SERS of DMAB reveals that the better experimental conditions for observing SERS signals of DMAB are (1) concentration of PATP is around 5 x 10(-6) M in which condition the aggregates consist with about 3-5 silver nanoparticles, which are not too big and suitable for SERS measurement, and (2) the Raman signal will be strongest at the time delay about 27 min for this concentration. By analyzing the symmetry of strong enhanced vibrational modes, it is derived that all of six strong vibrational modes are mostly enhanced by surface plasmons (electromagnetic field). The SERS enhancement calculated with finite-difference time-domain method is on the order of |M|(4) = 9.0 x 10(8) in junctions of AgNPs at 632.8 nm, where |M| = E(loc)/E(in), and E(loc) and E(in) are local and incident electric fields, respectively. The total chemical enhancements, including static chemical and resonant enhancements, are on the order of 10(3).

Hydrophobic Modification of Ti-Containing Zeolite (TS-1) and Their Applications in Liquid-Phase Selective Catalytic Reactions

Abstract Hydrophobic modification of Ti-containing zeolite (TS-1) was performed by using triethoxyfluorosilane (TEFS). TS-1 after modification with TEFS (w = 1%) showed higher catalytic activity for the ammoximation of cyclohexanone than those on unmodified and modified TS-1 with TEFS (w = 5%) due to effective modification without covering the underlying catalytically active Ti-oxide species.

The influence of lattice oxygen in titania on selective catalytic reduction in the low temperature region

Vanadia/titania catalysts have various NOx conversion capabilities, which are dependent on the titania support, in selective catalytic reduction reactions with ammonia in the low temperature region. Because oxygen is an essential component in standard SCR reactions, the ability to provide lattice oxygen is an important factor dictating catalytic activity. Lattice oxygen can be provided to the reactants from a vanadia support as well as from a titania support. When the lattice oxygen in vanadia is exhausted, lattice oxygen in titanium can be supplied to vanadium; through this transfer of lattice oxygen, the SCR reaction can continue to proceed and an oxygen bridge between vanadium and titanium can be formed. Therefore, titania supports containing O/Ti mole ratios varying from 1.8 to 2.0 without vanadium deposition were adequate as SCR catalysts. In this work, the dual site mechanism was modified; based on these findings a more detail mechanism is suggested.