LaCoO3在含氧气氛下对CO还原SO2的催化性能

LaCoO3为CO还原SO2的催化剂,考察了催化剂用量、反应温度的影响以及混合催化剂对于CO还原SO2的催化作用。证实了催化活性相为La2O2S和CoS2相,并且通过XRD谱图的对比,初步探讨了催化剂的失活原因,以及O2对CO还原SO2反应和催化剂的影响。     

The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

The NO x reduction mechanism by H2 under near isothermal conditions over Pt–Ba/Al2O3 Lean NO x Trap systems

The study of the gas-phase NO reduction by H₂ and of the stability/reactivity of NO _x stored over Pt–Ba/Al₂O₃ Lean NO _x Trap systems allowed to propose the occurrence of a reduction process of the stored nitrates occurring via to a Pt-catalyzed surface reaction which does not involve, as a preliminary step, the thermal decomposition of the adsorbed NO _x species.     

Structural regeneration of LaCoO3 perovskite-based catalysts during the NO + H2 + O2 reactions

In situ X-ray diffraction (XRD) analysis was used to investigate structural evolutions of LaCoO₃ catalysts and then further modified by palladium (Pd) addition, under various controlled atmospheres, particularly during the reduction of NO by hydrogen in lean conditions. Complementary, XPS measurements provided information about changes in the chemical environments of Pd, Co and nitrogen during sequential temperature-programmed reactions. A preactivation thermal treatment under hydrogen led to the destruction of the perovskite structure while in the course of the NO + H₂ + O₂ reactions, the regeneration of the perovskite structure evidenced by XRD at 873 K started at lower temperature (573 K) at the surface. Palladium has been incorporated in order to evidence its effective role in the surface modifications of LaCoO₃ and its consequence on the catalytic activity.     

H_2O和SO_2对甲烷在金属铁表面还原NO的影响

为考察烟气中H2O和SO2对甲烷在金属铁表面还原NO的影响,采用程序控温电加热水平陶瓷管反应器,在N2气氛和模拟烟气气氛中、300~1100℃下进行了脱硝实验研究,并对反应后铁样品的组成进行了X光衍射(XRD)、场发射扫描电镜(ESEM)和X射线能谱(EDX)分析。结果表明:在N2气氛中H2O及SO2在高温下与NO竞争和金属铁反应,对金属铁还原NO有轻微的抑制作用。在加入甲烷的模拟烟气中,H2O和SO2共存对甲烷在金属铁表面还原NO有一定促进作用。水蒸气在高温下对金属铁的氧化过程中,会生成更多相对疏松的Fe2O3氧化层,有利于NO向内扩散与金属铁反应。加入7%H2O和0.02%SO2的模拟烟气,反应段过量空气系数SR1=0.7和燃烬段过量空气系数SR2=1.2时,在1000℃,有、无H2O及SO2时脱硝效率分别为96.9%和90.6%。     

Steam effect on NO x reduction over lean NO x trap Pt–BaO/Al2O3 model catalyst

The effect of steam on NO _x reduction over lean NO _x trap (LNT) Pt–Ba/Al₂O₃ and Pt/Al₂O₃ model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using CO and C₃H₈ as reductants, respectively. Compared to dry atmosphere, steam promoted NO _x reduction; however, under rich conditions the primary reduction product was NH₃. The results of NO _x reduction and NH₃ selectivity versus temperature, combined with temperature programmed reduction of stored NO _x over Pt–BaO/Al₂O₃ suggest that steam causes NH₃ formation over Pt sites via reduction of NO _x by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C₃H₈/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO, but also the stored NO _x contributed to NH₃ formation. The NH₃ formed under these conditions could be effectively trapped by a downstream bed of Co²⁺ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO _x reduction, leading to improved NO _x storage efficiency.     

ZrO2-Al2O3复合载体负载Ni基催化剂COx甲烷化性能

采用浸渍和粉末压片的方法制备了两种ZrO₂-Al₂O₃复合载体并用于负载Ni基催化剂,并利用氮气等温物理吸附、X射线粉末衍射（XRD）、H₂程序升温还原（H₂-TPR）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）等分析手段对催化剂物化性质进行表征,考察了ZrO₂-Al₂O₃复合载体制备方法及ZrO₂的引入对Ni基催化剂在CO、CO₂和CO-CO₂共存的3种体系下甲烷化反应活性的影响。材料表征和活性测试结果表明,在CO甲烷化体系中,与单一Al₂O₃载体相比,引入ZrO₂的复合载体能有效提高催化剂中Ni物种的分散度从而增强CO甲烷化过程中催化剂活性,且粉末压片法较浸渍法制备的复合载体能有效提高催化剂的还原度,降低还原温度,但前者会大大降低催化剂的比表面积;在CO₂甲烷化体系中,当载体形貌和制备方法相同时,载体的变化对催化剂活性的影响较小,CO₂转化率主要受到制备方法不同引起的物理性质如比表面积变化的影响;在CO-CO₂共存体系中,由于CO在竞争吸附中比CO₂更容易占据活性位点,所以呈现出优先进行CO甲烷化再进行CO₂甲烷化、CO₂的含量先增多后减少的规律。     

Numerical Analysis on the Characteristics of Soot Particles in C2H4/CO2/O2/N2 Combustion

The purpose of this study is to investigate the characteristics of soot particles in C₂H₄/CO₂/O₂/N₂ combustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO₂/O₂/N₂ mixture, the key species C₂H₂, C₃H₃ responsible for formation of first aromatic ring, the typical aromatics and 4-ring aromatics total production rate all decrease greatly. In addition, with CO₂ mole fraction from 0.2 to 0.5 in the mixture, the soot particle number density, volume fraction, surface area density, which are three most important parameters to soot particle property, are suppressed obviously. Furthermore, the increasing content of CO₂ in the oxidizer influences mostly H, OH radical concentrations by two reactions: CO+OH=CO₂ H and H+O₂=O+OH, and the production rate of H, OH from the two reactions declined, which revealed that CO₂ in mixture has an inhibiting effect on soot particle generation.     

H2-Induced NO x Adsorption/Desorption over Ag/Al2O3: Transient Experiments and TPD Study

NO adsorption/desorption over 1 wt% Ag/Al₂O₃ was studied by a combination of isothermal transient adsorption/desorption and NO _x temperature-programmed desorption (NO _x -TPD) methods. NO _x -TPD profiles obtained for Ag/Al₂O₃ were identified by comparison with decomposition profiles of “model” AgNO₃/Al₂O₃ and Al(NO₃)₃/Al₂O₃ prepared by impregnation of Al₂O₃ with individual AgNO₃ and Al(NO₃)₃ compounds. The data obtained indicate that H₂-induced NO adsorption leads to the formation of surface Ag and Al-nitrates. Their accumulation on the catalyst surface is accompanied by an intensive NO₂ evolution, which proceeds primarily via reaction of surface nitrates with NO. Thus, NO₂ formation appears to result from an intrinsic stage of the H₂-induced NO _x adsorption process, rather than from the direct oxidation of NO by gaseous oxygen catalyzed by Ag.     

The role of SO2 in the reduction of NO by CO on La2O2S

The decomposition of NO and the reduction of NO by CO on La₂O₂S were studied using temperature-programmed reaction technique coupled with fast mass spectrometry, powder X-ray diffraction and X-ray photoelectron spectroscopy. The role of SO₂ plays in the reduction is explored. It is found that the decomposition of NO is a favorable reaction step for the reduction of NO by CO achieved through a sulfur-assisted path. The oxygen produced in the decomposition is removed by the sulfur in the oxysulfide as SO₂, which in turn is reduced back to sulfur by CO on La₂O₂S. An external supply of sulfur, such as SO₂, in the feed is needed to maintain the population of sulfur in the oxysulfide and thus make the reduction sustainable.     

FTIR studies on the CO,CO2 and H2 co-adsorption over Ru-RuO x /TiO2 catalyst

FTIR spectra of a Ru-RuO_x/TiO₂ catalyst obtained on co-adsorption of CO, CO₂ and H₂ in the temperature range of 300–500 K were found to be the sum total of corresponding spectra observed during methanation of individual oxides. The two oxides compete for metal sites and at each temperature they reacted simultaneously to form distinct transient Ru(CO)_n type species even though the nature, the stability and the reactivity of these species were different in the two cases. The monocarbonyl species formed during adsorption/reaction of CO alone or of CO + H₂ were bonded more strongly than those formed during CO₂ + H₂ reaction.     

Competitive adsorption of NO,SO2 and H2O onto mordenite synthesized from perlite

A new material, mordenite synthesized from volcanic ash (perlite) in the presence of sodium salts, has been shown to be a weak sorbent for NO and a strong and reversible sorbent for SO₂. The mordenite's capacity to adsorb SO₂ was found to be related to the amount of sodium present in the material. Capacities as high as 8 wt% were achieved at 1250 ppm of SO₂ in helium at 25°C. In multicycle tests the mordenite maintained its capacity after more than 40 cycles when desorbing the SO₂ at 300°C. The adsorption rate of SO₂ in the absence of water was modelled and the adsorption activation energy was found to be 3.2 kcal mol⁻¹. Water significantly decreased the mordenite's capacity to adsorb SO₂ and also caused the SO₂ to be chromatographically desorbed in a roll-up peak. In these water-SO₂ adsorption experiments a peculiar breakthrough was observed for water, where the water concentration exiting the bed first decreased and then increased. This peculiar water breakthrough could not be explained by assuming independent adsorption of the two species, but was qualitatively predicted by assuming that water adsorption is enhanced by the presence of adsorbed SO₂.     

Effect of Low Concentration of SO x on NO Reduction with Propene Over Ag/Al2O3

Catalytic activity for NO reduction with propene was investigated at 0–80 ppm SO₂. NO was reduced more efficiently by propene on SO₂-treated than untreated catalyst. Simultaneously, combustion of reductant was observed to lower NO reduction efficiency. Thus, the role of surface-adsorbed SO _x species was regarded as depressing reductant combustion. NH₃ adsorption revealed that SO₂ treatment increased Bronsted acidity of the Ag/Al₂O₃ catalyst, which promoted propene activation. Reductant activation is a more important step, compared with NO activation to oxidative nitrate species. The NCO species, an index intermediate in NO _x reduction, was produced on SO₂-adsorbed Ag/Al₂O₃ at a lower temperature (473 K) than on the untreated catalyst. The reductive intermediates at low temperature are suggested to be alcohol, or aldehyde-adsorbed species, based on observed C=O band.     

The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 Over Sr-Promoted La2O3

The influence of CO₂ and H₂O on the activity of 4% Sr-La₂O₃ mimics that observed with pure La₂O₃, and a reversible inhibition of the rate is observed. CO₂ causes a greater effect, with decreases in rate of about 65% with O₂ present and 90% in its absence, while with H₂O in the feed, the rate decreased around 35-40% with O₂ present or absent. The influence of these two reaction products on kinetic behavior can be described by assuming competitive adsorption on the surface, incorporating adsorbed CO₂ and H₂O in the site balance, and using rate expressions previously proposed for this reaction over Sr-promoted La₂O₃. In the absence of O₂, the rate expression is $$r_{N_2 } = \frac{{k'P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }},$$ which yields a good fit to the experimental data and gives optimized equilibrium adsorption constants that demonstrate thermodynamic consistency. With O₂ in the feed, nondifferential changes in reactant concentrations through the reactor bed were accounted for by assuming integral reactor behavior and simultaneously considering both CH₄ combustion and CH₄ reduction of NO, which provided the following rate law for total CH₄ disappearance: $$(r_{{\text{CH}}_{\text{4}} } )_{\text{T}} = \frac{{k'_{{\text{com}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} + k'_{{\text{NO}}} P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }}.$$ The second term of this expression represents N₂ formation, and it again fit the experimental data well. The fitting constants in the denominator, which correspond to equilibrium adsorption constants, were not only thermodynamically consistent but also provided entropies and enthalpies of adsorption that were similar to values obtained with other La₂O₃-based catalysts. Apparent activation energies typically ranged from 23 to 28 kcal/mol with O₂ absent and 31-36 kcal/mol with O₂ in the feed. With CO₂ in the feed, but no O₂, the activation energy for the formation of a methyl group via interaction of CH₄ with adsorbed NO was determined to be 35 kcal/mol.     

CO3O4/MPS催化氧化NO性能

微乳法制备的介孔二氧化硅（MPS）负载Co3O4构成了Co3O4/MPS催化剂,考察了负载量、焙烧温度等制备条件和反应温度、空速、NO进口浓度、O2体积分数等操作条件对Co3O4/MPS催化氧化NO性能的影响,并对载体及催化剂进行了BET和XRD表征。结果表明：MPS比表面积远大于其它载体,Co3O4呈立方晶型,MPS负载25%的Co3O4在300 ℃下焙烧3 h得到催化剂的晶体颗粒最小,分散性好,具有最佳催化氧化活性和良好的稳定性,在NO进口浓度500 μL/L、O2体积分数10%、空速12 000 h－1的条件下,250 ℃时NO氧化率可达50%～60%（此时可获得最高的NOx吸收效率）,300 ℃氧化率达到80%以上,接近热力学平衡值。     

Adsorption of Some Atmospherically Important Molecules onto Large Water Clusters: SO2, SO3, HCl,and ClONO2

The adsorption of a range of atmospherically important molecules (SO₂, SO₃, HCl, and ClONO₂) on large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50–450 water molecules. SO₂ and HCl were found to stick with low efficiency to the water cluster, retaining their chemical identity. In contrast, both SO₃ and ClONO₂ undergo heterogeneous reactions on the surface of the water cluster forming, respectively, H₂SO₄ and HOCl with HNO₃. For SO₃, calculations show that the large barrier that exists in the gas-phase to the reaction of SO₃ with water is removed for water clusters of a sufficient size because of stabilization of the transition state by solvation. For ClONO₂, the barrier to reaction is much larger and cannot be removed by solvation for any size cluster. In this case, it is likely that reaction takes place on the water cluster by the ionic dissociation of ClONO₂ in a similar manner to that observed for ClONO₂ on ice films.     

十水合硫酸钠及十水合碳酸钠热导率的测量研究

用热敏电阻作加热元件和测温元件,首次系统测定了适合用作相变储热材料的十水合硫酸钠、十水合碳酸钠在温度范围10～80℃的热导率,两者实验热导率的偏差率分别为:±2.56%和±2.41%。同时,报道了十水合硫酸钠、十水合碳酸钠在实验中观测到的熔点分别为30℃和30℃,这些测量值与文献值基本吻合。     

NO2-aided Soot Oxidation on LaMn0.7Ni0.3O3 Perovkite-type Catalyst

The LaMnO₃-based perovskite-type mixed oxides were studied for both trapping of NO _x and combustion of diesel soot. The LaMn_0.7Ni_0.3O₃ (LMN3) perovskite shows high NO _x adsorption capacity, quick adsorption rate and efficient adsorbed species. After the catalyst interacts with NO at low temperature around 325 °C, decomposition of the nitrates leads to the decrease of the maximum soot oxidation temperature to 430 °C. The fine crystallite size, increased surface area and readily reducibility at low temperature also favor the oxidation of soot over LMN3 under loose contact conditions.