Investigation of the common intermediates over Fe-ZSM-5 in NH 3-SCR reaction at low temperature by in situ DRIFTS

The surface species formed in the reaction of NO and NO2 with pre-adsorbed NH 3 over a Fe-ZSM-5 catalyst(1.27 wt.%Fe,SiO2/Al2O3=25)at low temperature(140°C)were studied by in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS).Through using a background spectrum of NH3-saturated Fe-ZSM-5,we clearly observed the formation of common intermediates resulting from the reaction of NO2 or NO+O2 with pre-adsorbed NH3.This presents strong evidence that the oxidation of NO to form surface nitrates and nitrites is the key step for standard SCR at low temperature.In addition,the results suggest that in the SCR reaction at low temperature,the NH^4+ions absorbed on Brønsted acid sites are less active than NH3 adsorbed on Lewis acid sites related to Fe species.

Construction of Cu-Ce interface for boosting toluene oxidation:Study of Cu-Ce interaction and intermediates identified by in situ DRIFTS

A facile hydrothermal method was applied to gain stably and highly efficient CuO-CeO_(2)(denoted as Cu1Ce2)catalyst for toluene oxidation.The changes of surface and inter properties on Cu1Ce2 were investigated comparing with pure CeO_(2)and pure CuO.The formation of Cu-Ce interface promotes the electron transfer between Cu and Ce through Cu^(2+)+Ce^(3+)↔Cu^(+)+Ce^(4+)and leads to high redox properties and mobility of oxygen species.Thus,the Cu1Ce2 catalyst makes up the shortcoming of CeO_(2)and CuO and achieved high catalytic performance with T_(50)=234°C and T_(99)=250°C(the temperature at which 50%and 90%C_(7)H_(8)conversion is obtained,respectively)for toluene oxidation.Different reaction steps and intermediates for toluene oxidation over Cu1Ce2,CeO_(2)and CuO were detected by in situ DRIFTS,the fast benzyl species conversion and preferential transformation of benzoates into carbonates through C=C breaking over Cu1Ce2 should accelerate the reaction.

In situ DRIFTS study of NO_x adsorption behavior on Ba/CeO_2 catalysts

A series of Ba/CeO2 catalysts with different Ba loading amounts were prepared by incipient wetness impregnation. Their NOx adsorption behaviors under NO and NO＋O2 conditions were investigated by in situ DRIFTS. It was found that NOx was ad-sorbed and stored in the form of nitrites and nitrates on both Ba and Ce sites on the surface of the catalysts. The less thermally stable BaCO3 was suggested to be the main active phase for NOx trapping. Ceria served primarily as an oxygen supplier in the absence of O2, and the reaction from nitrites to nitrates on Ba sites was the key step in this case. In the presence of O2, however, gaseous O2 became the main oxygen source. The NOx adsorption capacity of the catalyst was dominated by the Ba content. Moreover, the stability of ni-trites and nitrates formed on Ce sites was found to be lower than those formed on Ba sites which existed in the form of the ionic bar-ium nitrate species.

Highly efficient photocatalytic NO removal and in situ DRIFTS investigation on SrSn(OH)_(6)

A novel SrSn(OH)_(6) photocatalyst with large plate and particle size were synthesized via a facile chemical precipitation method. The photocatalytic activity of the SrSn(OH)_(6) was evaluated by the removal of NO at ppb level under UV light irradiation. Based on the ESR measurements, SrSn(OH)_(6) photocatalyst was found to have the ability to generate the main active species of O_(2)^(·-), ^(·)OH and ^(1)O_(2) during the photocatalytic process. Moreover, SrSn(OH)_(6) photocatalyst not only exhibits high photocatalytic activity for NO removal (79.6%), but also has good stability after five cycles. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the NO_(x) transfer pathway and the intermediate products distribution during the adsorption and photocatalytic NO oxidation process. The present work not only provides an efficient material for air pollutants purification at room temperature but also in-depth understanding of the mechanism involved in the photocatalytic NO removal process.

Elimination of formaldehyde over Cu-Al_2O_3 catalyst at room temperature

Catalytic elimination of formaldehyde(HCHO) was investigated over Cu-Al_2O_3 catalyst at room temperature. The results indicated that no oxidation of HCHO into CO_2 occurs at room temperature, but the adsorption of HCHO occurs on the catalyst surface. With the increase of gas hourly space velocity(GHSV) and inlet HCHO concentration, the time to reach saturation was shortened proportionally. The results of the in situ DRIFTS, Density functional theory calculations and temperature programmed desorption(TPD) showed that HCHO was completely oxidized into HCOOH over Cu-Al_2O_3 at room temperature. With increasing the temperature in a flow of helium, HCOOH was completely decomposed into CO_2 over the catalyst surface, and the deactivated Cu-Al_2O_3 is regenerated at the same time. In addition, although Cu had no obvious influence on the adsorption of HCHO on Al_2O_3, Cu dramatically lowered the decomposition temperature of HCOOH into CO_2. It was shown that Cu-Al_2O_3 catalyst had a good ability for the removal of HCHO, and appeared to be promising for its application in destroying HCHO at room temperature.

Mechanistic Drifting Forecast Model for A Small Semi-Submersible Drifter Under Tide–Wind–Wave Conditions

Understanding the drifting motion of a small semi-submersible drifter is of vital importance regarding monitoring surface currents and the floating pollutants in coastal regions. This work addresses this issue by establishing a mechanistic drifting forecast model based on kinetic analysis. Taking tide–wind–wave into consideration, the forecast model is validated against in situ drifting experiment in the Radial Sand Ridges. Model results show good performance with respect to the measured drifting features, characterized by migrating back and forth twice a day with daily downwind displacements. Trajectory models are used to evaluate the influence of the individual hydrodynamic forcing. The tidal current is the fundamental dynamic condition in the Radial Sand Ridges and has the greatest impact on the drifting distance. However, it loses its leading position in the field of the daily displacement of the used drifter. The simulations reveal that different hydrodynamic forces dominate the daily displacement of the used drifter at different wind scales. The wave-induced mass transport has the greatest influence on the daily displacement at Beaufort wind scale 5–6; while wind drag contributes mostly at wind scale 2–4.

Large anisotropic negative thermal expansion in Cu-TDPAT metalorganic framework:A combined in situ X-ray diffraction and DRIFTS study

Cu-TDPAT(H_(6)TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation processes.In this work,in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion(NTE).The PASCal crystallography tool,used to analyze the magnitude of the NTE,reveals an average volumetric thermal expansion coefficientαv=-20.3 MK^(-1).This value is significantly higher than the one reported for Cu-BTC(also known as HKUST-1),which contains the same Cu-paddlewheel building unit,αv=-12 MK^(-1).In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were employed to shed light on the NTE mechanism.Using these two methods,we were able to elucidate the three main structural motions that are responsible for the NTE effect.The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC.The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.

改性沸石咪唑催化剂的NH_(3)-SCR催化性能研究

通过微波法合成了沸石咪唑骨架结构材料ZIF-7,并以ZIF-7为前驱体制备了CuCe@ZIF-7催化剂。通过固定床实验平台测试了制备条件、反应温度、催化剂用量、SO_(2)、H_(2)O等实验条件对催化剂NH_(3)-SCR催化性能的影响,通过XRD、SEM、XPS、TG等表征研究了CuCe@ZIF-7理化性质,并通过in situ DRIFTS研究了催化剂的反应机理。

CuFe_(2)O_(4)催化剂的制备及其NH_(3)-SCR催化性能研究

通过微波法合成了金属有机骨架材料Cu-MIL-101(Fe),然后以此为前驱体煅烧制备了CuFe_(2)O_(4)催化剂,并考察了反应温度、催化剂用量、空速、SO_(2)、H_(2)O等因素对催化剂NH_(3)-SCR催化性能的影响。测试结果表明CuFe_(2)O_(4)催化剂可以在250~450℃的宽温度区间保持90%以上的脱硝效率,反应前后催化剂无明显变化,同时in situ DRIFTS光谱结果表明,CuFe_(2)O_(4)催化剂在脱硝过程中同时存在L-H以及E-R两种反应机理。

Effect of Ni particle size on the production of renewable methane from CO_(2) over Ni/CeO_(2) catalyst

Production of’renewable Methane’has attracted renewed research interest as a fundamental probe reaction and process for CO_(2)utilization through potential use in Cl fuel production and even for future space exploration technologies.CO_(2)methanation is a structure sensitive reaction on Ni/CeO_(2)catalysts.To precisely elucidate the size effect of the Ni metal center on the CO_(2)methanation performance,we prepared2%Ni/CeO_(2)catalysts with pre-synthesized uniform Ni particles(2,4 and 8 nm)on a high surface area CeO_(2)support.Transmission electron microscopy(TEM)and ambient pressure X-ray photo spectroscopy(AP-XPS)characterization have confirmed that the catalyst structure and chemical state was uniform and stable under reaction conditions.The 8 nm sized catalyst showed superior methanation selectivity over the 4 and 2 nm counterparts,and the methanation activity in term of TOF is 10 times and 70 times higher than for the 4 and 2 nm counterparts,respectively.The DRIFTS studies revealed that the larger Ni(8 nm particles)over CeO_(2)efficiently facilitated the hydrogenation of the surface formate intermediates,which is proposed as the rate determining step accounting for the excellent CO_(2)methanation performance.

Earth-Abundant CaCO_(3)-Based Photocatalyst for Enhanced ROS Production,Toxic By-Product Suppression,and Efficient NO Removal

Photoinduced reactive oxygen species(ROS)-based pollutant removal is one of the ideal solutions to achieve the conversion of solar energy into chemical energy and thus to address environmental pollution.Here,earthabundant CaCO_(3)-decorated g-C_(3)N_(4)(g-C_(3)N_(4)labeled as CN,CaCO_(3)-decorated g-C_(3)N_(4)sample labeled as CN-CCO)has been constructed by a facile thermal polymerization method for safe and efficient photocatalytic NO removal.The decorated CaCO_(3)as“transit hub”extends theπbonds of CN to deviate from the planes and steers the random charge carriers,which thus provides extra active sites and expedites spatial charge separation to facilitate adsorption/activation of reactants and promote formation of ROS participating in the removal of pollutant.Furthermore,boosted generation of ROS regulates the photocatalytic NO oxidation pathway and thus increases the selectivity of products.NO prefers to be directly oxidized into final product(nitrate)rather than toxic intermediates(NO_(2)),which is well demonstrated by theoretically simulated ROS-based reaction pathways and experimental characterization.The present work promotes the degradation of pollutant and simultaneously suppresses the formation of toxic by-product,which paves the way for ROS-based pollutant removal.

Performance and mechanism study for low-temperature SCR of NO with propylene in excess oxygen over Pt/TiO_2 catalyst

A 0.5 wt.% Pt/TiO2 catalyst was prepared and used for the low-temperature selective catalytic reduction （SCR） of NO with C3H6 in the presence of excess oxygen. The effects of Pt loading and 02 concentration on Pt/TiO2 catalytic performance for low-temperature SCR were investigated. It was found that optimal Pt loading was 0.5 wt.% and excess 02 favored low-temperature SCR of NOx. The mechanism of low-temperature SCR of NO with C3H6 was investigated with respect to the behavior of adsorbed species over Pt/TiO2 at 150~C using in situ DRIFTS. The results indicated that surface nitrosyl species （Pt~＋-NO and Ti3＋-NO） and pt2＋-CO are main reaction intermediates during the interactions of NO, C3H6 and 02. A simplified NO decomposition mechanism for the low-temperature SCR of NO with C3H6 was proposed.

Self-doped Br in Bi_(5)O_(7)Br ultrathin nanotubes:Efficient photocatalytic NO purification and mechanism investigation

Bismuth-rich Bi_(5)O_(7)Br is a promising photocatalyst for pollutant removal owing to its stability and appropriate band structure in comparison with bismuth oxybromide.However,bulk-phase Bi_(5)O_(7)Br suffers from poor light absorption and high charge recombination rates resulting in poor activity.Elemental doping is a powerful strategy to enhance photocatalytic activity.In this study,we prepared a series of Br autodoped ultrathin Bi_(5)O_(7)Br nanotubes and explored the effect of Br doping on photocatalytic NO removal.The optimal doping content was determined via a photocatalytic NO removal experiment,which revealed the optimal ratio of Bi and Br was approximately 3:1.In situ diffuse reflectance infrared Fourier transform spectroscopy(In situ DRIFT)and density functional theory(DFT)studies revealed that NO removal mechanism catalyzed by Br doped Bi_(5)O_(7)Br.Our work presents a new strategy for the enhancement of photocatalytic pollutant degradation by bismuth oxyhalide photocatalysts.

Enhancement of toluene oxidation performance over La_(1-x)CoO_(3-δ) perovskite by lanthanum non-stoichiometry

La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.

Selective catalytic reduction of NO_(x) with NH_(3) over core-shell Ce@W catalyst

An environmentally benign WO_(3) wrapped cubic CeO_(2) core-shell catalyst(Ce@W)was developed for the selective catalytic reduction of NO_(x) with NH_(3).Compared with CeW particles prepared via the conventional co-precipitation method,this core-shell catalyst not only displays higher tolerance to SO_(2) and H_(2)O,but also exhibits a wider activity tempe rature window of 250-450℃,in which NO_(x)conversion and N_(2) selectivity reaches 100%.The improved performance of Ce@W catalysts can be contributed to the strong interactions between CeO_(2)(100) and WO_(3),which generates more Ce^(3+) and surface chemisorbed oxygen.In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTs)reveal that the more thermally stable Br?nsted acid sites on Ce@W lead to its excellent high-temperature activity.

Promotional mechanism of activity of CeEuMnO_(x) ternary oxide for low temperature SCR of NO_(x)

Due to strong synergistic effect of the elements,a series of XEuMnO_(x) ternary oxides(X=Ce,Ni,Co,Sb,Sn,Mo) were synthesized by one-pot co-precipitation method,and composite components were identified and optimized to maintain high activity and superior SO_(2)and H_(2)O endurance in selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR).NO_(x)conversion of CeEuMnO_(x) ternary oxide catalysts attains more than 90% at 100-250℃,and finally achieves 74%under existence of 50×10^(-6)SO_(2) and 10 vol% H_(2)O at 230℃.The facile electron transfer through redox cycle of Mn^(3+)+Ce^(4+)■Mn4++Ce^(3+) and enhanced oxygen mobility can promote formation of more Mn species in high oxidation state and chemisorbed oxygen,accelerating oxidation of NO and the adsorbed NO_(2) formed can facilitate"fast SCR"reaction to improve low-temperature activity.In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)study reveals that addition of Ce to EuMnO_(x)catalyst boosts adsorption of NH_(3)and NO_(x)species.NH_(3)species are activated as crucial intermediate(NH_(2))to promote NH_(3)-SCR reaction.This research provides a novel material for practical deNO_(x)application of stationary source combustion flue gas in the future.