Effect of hydrocarbon species on no oxidation over diesel oxidation catalysts

The effect of propylene concentration on NO oxidation as a function of temperature and position over a model Pt-Pd/Al₂O₃ diesel oxidation catalyst was investigated. Propylene had an apparent inhibition effect on NO oxidation. This apparent inhibition is a result of NO₂, as the NO oxidation product, acting as an oxidant in the reaction with propylene. This was verified with experiments that included NO₂, and a resulting significant temperature decrease in the onset of NO₂ reduction when propylene was present. Furthermore, increasing amounts of propylene further decreased the NO₂ reduction temperature. Similar results were observed with m-xylene and dodecane addition as well. The results also demonstrate that NO₂ was consumed preferentially relative to O₂ during hydrocarbon oxidation. With low inlet levels of O₂, the addition of NO₂ apparently inhibited propylene oxidation after the onset of NO₂ reduction. This subsequent inhibition was due to the NO formed, demonstrating that propylene results in reduced NO₂ outlet levels while NO inhibits propylene oxidation.     

Hydrocarbon storage modeling for diesel oxidation catalysts

A simple hydrocarbon (HC) storage model was proposed which represents the adsorption-desorption processes in zeolites incorporated in a diesel oxidation catalyst (DOC). Using four experiments in which the HC was stepped up and the reactor run until steady state, a Langmuir isotherm was generated that was sufficient to represent the equilibrium data, and the remaining rate constant capturing the adsorption time scale was obtained by fitting. The model thus developed was validated using reactor data which was obtained by stepping the inlet HC concentration to zero after outlet reached equilibrium.A typical DOC which contained both a storage component (zeolite) and noble metal component (for oxidation) was studied using a full scale 1D reactor model which includes the storage kinetics developed here with the oxidation kinetics developed in our previous work [Sampara et al., 2008. Global kinetics for a commercial diesel oxidation catalyst with two exhaust hydrocarbons. Industrial & Engineering Chemistry Research 47, 311-322]. Simulations of a simplified warm-up process indicated that the zeolite storage component reduces the overall cold start HC emissions by at least a factor of two if the warm-up rate achieves , a range commonly observed during start-up. Modeling results also showed that the HC oxidation for these reactors commonly starts at the rear end of the reactor due to reduced CO inhibition. The rates of the individual processes during cold start were analyzed in detail and compared with the rate of inlet temperature increase provided from the exhaust.     

含CeO2催化剂用于柴油车尾气炭烟氧化的研究

采用共沉淀法合成含CeO₂催化剂M-Ce-O（M＝Fe、Cu、Zn、Co、Ni、Mn）和纯CeO₂,对催化剂进行TPO活性测试及BET、XRD、FT-IR和H2 -TPR表征。结果表明,在Ce中添加过渡金属,改变了CeO₂的晶相结构,比表面积增大,催化剂促进炭烟的燃烧,其促进炭烟氧化的活性顺序为：Ni-Ce-O＞Mn-Ce-O＞Cu-Ce-O＞Fe-Ce-O＞Ce-O＞Co-Ce-O＞Zn-Ce-O,其中,Ni-Ce-O表现出较高的活性,对应起燃温度降至340 ℃。TPR表明,催化活性与500 ℃以下的表面可还原氧量相关。     

水热催化制备绿色柴油工艺中催化剂的失活与再生

近年来,水热催化制备绿色柴油的工艺广受关注,非均相催化剂用于该工艺可以提高绿色柴油的产率和选择性,但催化剂使用过程中常存在失活和再生困难等问题。本文首先介绍了水热催化工艺中常用的催化剂,随后阐述了该工艺中非均相催化剂的失活机理;分别讨论了负载金属和载体对催化剂活性的影响。负载金属的浸出和烧结是引起催化剂失活的重要原因,载体自身不稳定是催化剂失活的另一个重要原因。然后,总结了水热催化工艺中失活催化剂的再生方法,主要包括煅烧和洗涤。最后,对水热催化制备绿色柴油工艺提出了建议,即开发更优质的催化剂、探求更高效的再生方法和选择更适宜的反应条件等。     

Zirconia supported Ru–Co bimetallic catalysts for diesel soot oxidation

Various amounts of ruthenia–cobaltate bimetallic catalyst supported on zirconia have been prepared by co-impregnation method and their catalytic activity towards soot/carbon oxidation has been evaluated using TG technique under the loose contact condition. These catalysts show good activity for carbon/soot oxidation, which is observed to be a factor of ruthenia content. The thermal stability experiments confirmed the stability of catalytic materials in air at least up to 900 °C. In this way, ruthenia can be easily dispersed on zirconia possibly through the solid solution formation, while its thermal stability can be significantly improved by introducing a transition metal namely cobalt. Formation of Ru–Co bimetallic clusters over zirconia is probably responsible for its thermal stability, while dissociative adsorption of oxygen on catalyst surface appears to be responsible for their catalytic activity.     

Catalytic combustion of diesel soot: Deactivation by SO2 of copper and potassium nitrate catalysts supported on alumina

The SO₂ poisoning of Cu KNO₃/Al₂O₃ catalysts used in the catalytic combustion of diesel soot with NO/O₂ feed has been studied in this work. Fresh catalysts show temperatures of maximum combustion rate (T_max) at about 470, 375 and 368 °C for Cu/Al₂O₃, KNO₃/Al₂O₃ and Cu KNO₃/Al₂O₃ respectively. Poisoned catalysts decrease the activity and techniques of vibrational spectroscopy (FTIR) and temperature programmed reduction (TPR) suggest the KNO₃ loss and the formation of potassium sulfate in the mentioned poisoned catalysts.     

FCC催化剂失活与再生

论述了近年来国内外对FCC催化剂失活,特别是中毒和积炭失活的研究现状。重点论述了FCC平衡剂再生利用的发展,并对其前景进行了展望。     

柴油车DOC催化剂Pt/CeZrO2载体的制备及影响

分别用氢氧化钠（NaOH）、草酸（H₂C₂O₄）和碳酸钠（Na₂CO₃）为沉淀剂制备CeZrO₂固溶体,并以此为载体制备了Pt/CeZrO₂柴油车DOC催化剂,通过XRD、BET、H₂-TPR和催化氧化反应等手段对催化剂物理化学特性进行研究。结果发现,以NaOH作为沉淀剂制备的CeZrO₂固溶体比表面积大（68.8 m²·g^-1）、氧活动性强[表面氧耗氢量达1143 μmol·（g cat（^-1],同时贵金属Pt在其表面高度分散,因此制得的Pt/CeZrO₂柴油车DOC催化剂催化效果好,特别是催化氧化碳氢化合物（C₃H₆）,T₉₀比H₂C₂O₄和Na₂CO₃为沉淀剂制备的Pt/CeZrO₂催化剂降低了将近40℃。另外载体制备方式对催化剂抗硫性影响也十分显著。故选择一种合适的载体沉淀剂可使制得的DOC催化剂具备良好的活性及抗硫性。     

Turbulent operation of diesel oxidation catalysts for improved removal of particulate matter

This paper proposes that a diesel oxidation catalyst (DOC) operating within the fully turbulent flow regime is an efficient means of reducing the contents of particulate matter in the exhaust gases. The suggested mode of operation is in contrast to the fact that the DOCs are typically operated within the laminar flow regime. In the paper, the particle trapping efficiency and pollutant conversion in turbulent ceramic DOCs are calculated using both mass-transfer correlations available in the literature and computational fluid dynamics (CFD). It is shown that a turbulent DOC substantially increases the removal of small particulates from the exhaust gases. This indicates the potential of the aftertreatment system to comply with the forthcoming number-based emission legislations on particulate matter. In addition, the turbulent DOC can be used to optimize the overall performance of a combined system consisting of a DOC and a diesel particulate filter.     

直馏柴油催化氧化脱硫均相催化剂的制备与评价

引　言柴油脱硫技术分为加氢脱硫和非加氢脱硫两大类[1]. 传统的加氢工艺能够满足柴油的低硫要求,但存在装置投资大、操作条件苛刻 (温度>300 ℃,压力>4 0 MPa, 需要氢源) 和操作费用高等技术经济问题. 非加氢脱硫技术在常温或低温、常压和无须氢源条件下操作已受到国内外广泛的重视, 得到很大的发展. 非加氢脱硫技术主要有吸附法[1,2]、萃取法[3,4]、络合法[5]、生物脱硫法[6]、H2O2 氧化法[7,8] 和催化氧化法[9], 其中 H2O2 氧化法已成为国内外的研究热点, 如美国 Petro star公司、日本 PEC、中国石油大学、洛阳石化工程公司等均在大…     

Bimetallic Pt/Pd diesel oxidation catalysts: Structural characterisation and catalytic behaviour

Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies on supported bimetallic Pt/Pd diesel oxidation catalyst (Pt:Pd weight ratio 2:1) after various treatments were compared with those of monometallic Pd and Pt catalysts prepared under similar conditions. After calcination and thermal ageing, the coexistence of alloyed bimetallic Pt/Pd particles and of tetragonal PdO has been found in the bimetallic Pt/Pd catalyst. PdO is present in form of crystals at the surface of the Pt/Pd particles or as isolated PdO crystals on the support oxide. Bimetallic Pt/Pd nanoparticles were already formed in the Pt/Pd catalyst after calcination. Hydrogen treatment causes the formation of randomly alloyed Pt/Pd nanoparticles. In the thermally aged catalyst, a strong indication for an enrichment of Pt in the interior of the particle and of Pd at its outer shell was found. In the monometallic catalyst, the Pd is found to be completely oxidised already after calcination and to consist of metallic Pd in zero-valent state exclusively after reductive treatment. Ageing under hydrothermal oxidative atmosphere leads to complete oxidation of the Pd species. After calcinations, the catalytic activity of the Pt/Pd catalyst studied is comparable to those of monometallic Pt catalysts. In contrast to monometallic Pt catalysts, the alloyed system show significant stabilisation against sintering and a much higher activity after the thermal ageing step. This stabilisation of dispersion and the presence of Pt atoms on the surface of the Pt/Pd particles are considered to cause the higher catalytic activity of metallic particles for the oxidation of carbon monoxide and propene after ageing.     

Low-temperature activity for CO oxidation over diesel oxidation catalysts studied by High Throughput Screening and DRIFT spectroscopy

We have investigated the low-temperature activity for CO oxidation for a series of platinum catalysts supported on Al₂O₃, TiO₂, ZSM-5, CeO₂ and ZrO₂-CeO₂. The results show major differences in activity, due to the support for Pt, especially in the presence of water. Improved activity over ceria containing samples in presence of water is likely due to the water-gas shift (WGS) reaction. Studies with in situ IR spectroscopy suggest a surface formate mechanism for the WGS reaction on Pt/CeO₂.     

Testing molten metal oxide catalysts over structured ceramic substrates for diesel soot oxidation

Onboard tests of an oxide (CoO_x) and a molten mixed oxide catalyst (CoPbO_x) supported on cordierite wall flow filters (Corning Durotrap CO EX80) were performed on rollers with a 1.9-l light duty vehicle for three different driving conditions including two constant speeds with different loadings and a standard European cycle (NEDC). The balance point temperatures obtained in these tests were used to compare the catalytic activity under onboard conditions with laboratory measurements. Onboard tests showed similar catalytic activities with the previous micro-reactor experiments performed in “loose contact” mode [D. Uner, M.K. Demirkol, B. Dernaika, Appl. Catal. B: Environ., in press]. The concentration profiles of the active layer determined by SEM-EDX analysis after use and after aging revealed that the mobile component, PbO_x, migrated in the flow direction and accumulated at the closed end of the channel. There is no direct evidence for the evaporative loss of PbO_x. Regions of high activity indicated by low carbon amounts with unique Pb–Co ratios were determined by SEM analysis.     

Deactivation of hydrodesulfurization catalysts by metals deposition

Primary causes of deactivation of hydrodesulfurization catalysts are partial poisoning of the interior pore surface and pore-mouth plugging by deposition of metals from organo-metallic compounds in the reactor feed. A model is developed to account for both causes of deactivation. It can be used to predict which occurs first: complete surface poisoning or pore-mouth plugging. Equations are formulated for catalyst activity as a function of time for demetallization and also for desulfurization. The results depend upon particle geometry and geometry of deposited species, Thiele moduli for demetallization and desulfurization, and relative rates of desulfurization on fresh and partially poisoned catalytic surfaces. The treatment is for a single, isothermal catalyst particle.     

Deactivation of hydrodesulfurization catalysts during reactor startup

Metal sulfide catalysts for ultra-deep hydrodesulfurization of diesel generally lose a fraction of their catalytically active sites during reactor startup. The underlying mechanisms are discussed. A laboratory diagnostic tool consisting of three probe molecules is developed for testing metal sulfide catalysts' start-of-run (SOR) activity maintenance. It is found that a significant fraction of the active sites on a commercial supported catalyst are deactivated permanently, but this is not the case with a bulk metal sulfide catalyst. The SOR deactivation of the bulk catalyst is completely reversible, while that of the supported catalyst is partially reversible. The diagnostic tool may provide a basis for developing a high-throughput approach for evaluating and enhancing catalyst SOR stability, thereby increasing plant productivity.     

柴油加氢裂化装置加氢裂化催化剂失活分析

在某炼油厂柴油加氢裂化装置停工换剂时,取样分析加氢裂化催化剂。对所取裂化剂进行甲苯抽提、再生后,采用比表面积及孔径分析仪、碳硫分析仪(C-S)和X射线衍射仪(XRD)等手段进行检测。结果表明,失活裂化剂的比表面积、孔容等孔结构性能参数明显降低。在最优的再生条件下,再生裂化剂上的C含量降至0.360%,裂化剂的表面或其它位置未发现杂质的明显沉积。再生裂化剂的比表面积损失约21.5%,其中微孔比表面积的损失约占87.2%,孔容损失约17.4%。加氢裂化催化剂长期在高温等条件下反应,造成分子筛晶粒的烧结、团聚等是导致其比表面积等孔结构性能降低的主要原因。     

Deactivation of fixed-bed nickel hydrogenation catalysts by sulfur

A series of fixed-bed nickel hydrogenation catalysts was tested in the dearomatization of hydrocarbon solvents. The mechanism of catalyst deactivation by aromatic sulfur compounds was studied in high-pressure micro-flow equipment by variation of the experimental conditions and the sulfur content of the feed. It is concluded that catalyst deactivation proceeds under mild but realistic conditions through formation of a surface sulfide which blocks the active surface. The rate of the disappearance of the active sites is a first-order process with rate constant 1.0 × 10⁻³ (ppm S)⁻¹ h⁻¹. Under more severe conditions, more sulfide layers are formed, but bulk Ni₃S₂ was not observed even after full deactivation of the catalysts. The poisoning of the active sites in the latter case is no longer a first-order process. Consequently, under the circumstances investigated, the sulfur resistance of nickel catalysts is determined by the nickel surface area per unit weight of catalyst.