负载型NiO和CoO催化剂上N2O分解研究

本研究在对多种金属氧化物催化剂进行初步筛选的基础上，研制出以莫来石为载体的负载型NiO、CoO催化剂，考察了分解温度、催化剂组成和负载量对N2O分解率的影响，并对其分解反应动力学进行了研究。结果表明莫来石负载NiO、CoO催化剂对N2O分解有良好的催化性能；其反应速度对N2O均为一级反应；同样负载量下NiO有更好的催化分解活性；这一研究为开发阻力低、催化性能好的工业用蜂窝型规整填料奠定了基础。     

Catalytic decomposition of N2O over supported Rh catalysts: effects of supports and Rh dispersion

The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al₂O₃, ZrO₂, FSM-16, CeO₂, La₂O₃) showed that the activities of Rh/Al₂O₃ and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N₂O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N₂O experiment over a Rh/USY catalyst suggested that the catalytic N₂O decomposition occurs on oxygen-covered surface and that O₂ may be freed on collision of N₂O molecules with the adsorbed oxygen atoms.     

Co/RPSA系列催化剂在N2O分解中的应用

采用正交试验设计方法设计和浸渍法制备分子筛RPSA负载Co、K、Ba和Sr催化剂,使用微型反应器评价催化剂用于直接分解N₂O的催化活性,考察活性组分对催化剂活性的影响。采用XRD、H₂-TPR和NH₃-TPD等方法对催化剂进行表征。结果表明,金属Co和K对催化剂活性影响显著,Co对提高催化剂活性有促进作用,Co含量增加,催化剂活性提高,而K对催化剂活性有抑制作用。催化剂表征结果显示,Co物种主要以Co₃O₄形式存在于载体表面,催化剂的组成和配比影响催化剂活性、氧化还原性能和酸性,催化剂强酸的存在有利于催化剂活性的提高。
     

Catalytic decomposition of propellant N2O Over Ir/Al2O3 catalyst

N₂O, as a green propellant alternative to N₂H₄, shows potential application in satellite propulsion system. The state of Ir species and the reaction behaviors on Ir/Al₂O₃ in the oxidative environment during N₂O decomposition were identified here. Two types of Ir sites existed in this catalyst and affected the process of N₂O decomposition. The strong Ir sites facilitated the dissociative adsorption of N₂O to form N₂ and adsorbed O atoms with adsorption heat of as high as 281 kJ/mol, which promoted the desorption of adsorbed O atoms and favored the self‐sustaining decomposition of N₂O by raising the catalyst bed temperature. The other Ir sites interacted weakly with O atoms but facilitated their combination to form O₂. The Ir/Al₂O₃ catalyst then exhibited an excellent performance in initiating the decomposition of N₂O at low temperature of 200°C and good stability in 0.1 N microthruster for orbit adjustment and attitude control of satellite. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3973–3981, 2016     

Rh2O3/monoclinic CePO4 composite catalysts for N2O decomposition and CO oxidation

CePO_4(in particular,monoclinic CePO_4)has been rarely used to make supported catalysts.Herein,monoclinic CePO_4 nanoparticles were prepared by calcining hexagonal CePO_4 nanorods(prepared by precipitation)in air at 900℃.Monoclinic CePO_4 nanowires were prepared by calcining hexagonal CePO_4 nanowires(prepared by hydrothermal synthesis at 150℃)in air at 900℃.Both monoclinic CePO_4 materials were used to support Rh_2O_3 by impregnation using Rh(NO_3)_3 as a precursor(followed by calcination).The catalytic performance of Rh_2O_3/monoclinic CePO_4 composite materials in N_2O decomposition and CO oxidation was investigated.It was found that Rh_2O_3 supported on monoclinic CePO_4 nanowires was much more active than Rh_2O_3 supported on monoclinic CePO_4 nanoparticles.The stability of catalysts as a function of reaction time on stream was studied in both reactions.The influence of co-fed CO_2,O_2,and H_2O on the catalytic activity in N_2O decomposition was also studied.These catalysts were characterized by employing N_2 adsorption–desorption,ICP-OES,XRD,TEM,XPS,H_2-TPR,O_2-TPD,and CO_2-TPD.The correlation between physicochemical properties and catalytic properties was discussed.     

Catalytic decomposition of CH2Cl2 over supported Ru catalysts

Ru/TiO₂ and Ru/Al₂O₃ were prepared by wet impregnation of TiO₂ and Al₂O₃, and tested in the catalytic decomposition of dichloromethane (DCM). Ru/TiO₂ catalyst presents the higher activity than Ru/Al₂O₃ catalyst, with 50% and 90% conversion occurring at 235 and 267 °C, respectively. Moreover, the higher stability on Ru/TiO₂ catalyst is observed, which can be related to ready removal of Cl species produced during DCM decomposition. The chlorine uptake on Ru/TiO₂ catalyst is estimated at 240 °C to be 0.36 mmol Cl/g_cat, while on Ru/Al₂O₃, the value is 1.46 mmol Cl/g_cat.     

Rh/γ-Al2O3–sepiolite monolithic catalysts for decomposition of N2O traces

The behaviour of Rh/γ-AlO₃–sepiolite monolithic systems in the N₂O decomposition reaction using catalysts with rhodium contents between 0.2 and 0.8 wt.% were analysed. The observed increase of the catalytic activity with the metal loading was related to an enhancement in the number of active sites. The SEM–EDX results showed that rhodium was mainly located on the alumina particles. The variation of the reaction rate values with the inlet N₂O and O₂ concentrations, suggested an apparent first order equation with respect to N₂O and zero order for O₂. The presence of NH₃ traces or water vapour in the feed decreased the catalytic activity, probably due to the competitive adsorption of NH_x or OH species. The ammonia oxidation reaction took place, producing N₂O as a secondary product. The monolithic catalysts developed operate with a low pressure drop achieving a N₂O conversion higher than 90% at 773 K in the presence of oxygen, ammonia or water vapour in the stream.     

Room temperature decomposition of N2O in the presence of gaseous oxygen on prereduced Rh supported catalysts

The room temperature decomposition of N₂O over prereduced Rh‐based catalysts (Rh supported on ceria, zirconia and titania–alumina) is studied as a function of the oxygen content in the feed. Results indicate that Rh supported on titania–alumina shows lower degree of inhibition by gaseous oxygen on this reaction, attributed to the role of the metal particle–support interface region in the reaction. The effect of Rh loading and of the reaction temperature are consistent with the hypothesis. This revised version was published online in July 2006 with corrections to the Cover Date.     

A study on effect of Rh precursor and La addition on N2O decomposition over Rh catalyst

The decomposition of N₂O in the presence of oxygen was studied on Rh/CeO₂ and Rh/La₂O₃–CeO₂ catalysts prepared by wet impregnation method. The conversion of N₂O decomposition increased as the Rh loading increased, and the Rh-chloride catalyst showed a poor activity than the Rh-nitrate catalyst. XPS and IC/ICP analysis confirmed that the Rh-chloride catalyst's low activity caused since Rh-chloride catalyst had the some RhCl₃ species. N₂O decomposition rate over Rh/La₂O₃–CeO₂ catalysts decreased as the La loading increased due to the SMSI effect between Rh and CeO₂. H₂ TPR confirmed that the activity and reducibility of the catalyst were closely related.     

Catalytic decomposition of ammonia over fly ash supported Ru catalysts

Fly ash (FA), an industrial waste material, has been treated by physical and chemical methods. These materials were then employed as supports for preparation of Ru-based catalysts for H₂ generation from ammonia decomposition. The physicochemical properties of the supports and Ru-based catalysts were characterised using several techniques. The results revealed that the surface area of FA could be enhanced and thus improved the dispersion of Ru particles, resulting in higher catalytic activity. Ru/FA-800 exhibits the highest conversion due to higher surface loading of Ru, stronger NH₃ adsorption and least acid sites.     

Catalytic synthesis of methanethiol from methanol and carbon disulfide over KW/Al2O3 catalysts

A series of KW/γ-Al₂O₃ catalysts with varying K/W mole ratio were prepared for the synthesis of methanethiol from carbon disulfide and methanol, and characterized by N₂ adsorption–desorption, XRD and NH₃/CO₂-TPD techniques. Experimental results showed that the acidic and basic property of the catalyst plays a key role on the catalytic performance. It is shown that the conversion of CH₃OH is chiefly related to the acid sites, while the base sites of catalysts are favorable for the selectivity toward CH₃SH and hydrocarbons, but the strong base sites will restrain the selectivity toward CH₃SH. When the K/W mole ratio is K/W = 2/1 and the reaction temperature is at 603 K, the conversion of CH₃OH and the selectivity toward CH₃SH are 98.3 and 56.2%, respectively.     

铜锌掺杂的六铝酸盐分解N2O催化性能研究

采用共沉淀法制备了Cu和Zn取代六铝酸盐（LaCu_xZn_1-xAl₁₁O_19-δ,x=0、0.2、0.4、0.5、0.6、0.8、1.0）催化剂,通过XRD和BET等技术对催化剂进行表征,利用微型固定床反应器考察催化剂对N₂O的分解活性。结果表明,以(NH₄)₂CO₃为沉淀剂制备的催化剂在1 200 ℃焙烧4 h,可以形成完整的六铝酸盐晶型,Cu和Zn能够取代Al³⁺进入六铝酸盐晶体结构。LaCu_xZn_1-xAl₁₁O_19-δ催化剂对N₂O分解有较好的催化活性,其中,LaCu_0.8Zn_0.2Al₁₁O_19-δ活性较好。在LaCu_xZn_1-xAl₁₁O_19-δ六铝酸盐中,Cu为N₂O催化分解的主要活性元素,Zn有助于提高催化剂的稳定性,但由于六铝酸盐的特殊结构,Zn在催化剂中的作用较小。     

Propylene metathesis over Re2O7/Al2O3-B2O3 catalysts

A series of alumina aluminum borate (AAB) with various Al/B molar ratios were prepared by the coprecipitation method. The supported rhenium oxide catalysts with various contents of Re₂O₇ were also prepared by the impregnation method with perrhenic acid. The catalytic activity and stability of Re₂O₇/AAB catalysts for the reaction of propylene metathesis were tested in a fixed-bed microreactor. It was found that Re₂O₇/AAB is more active, stable and regenerable than Re₂O₇/Al₂O₃ for propylene metathesis. The optimum Al/B molar ratio was found to be in the range of 4–10.     

The effect of La2O3 on dynamic OSC over the Pd/OSC/Al2O3-based catalysts

In this study, fresh and aged Pd/(OSC–Al₂O₃) and Pd/(Al₂O₃–OSC–La₂O₃) metallic monoliths (OSC material Ce_0.75Zr_0.25O₂) were used to find out the effect of La₂O₃ on the catalyst behaviour in dynamic oxygen storage capacity (OSC) measurements. In addition, the interaction of CO, NO and O₂ reaction compounds over the studied catalysts was investigated in order to understand the effect of La₂O₃ in the oxidation and reduction reactions in lean automotive exhaust gas conditions. A FT-IR gas analyser was used to analyse the product gas composition. The presence of La₂O₃ on fresh and aged catalysts had negative effect on both the dynamic OSC and the activity of the catalyst. The reason for this is the different washcoat compositions between the studied catalysts which could explain the differences in BET surface areas.     

碱土金属修饰的Co/RPSA催化剂催化分解N2O

以RPSA分子筛为载体,采用浸渍法制备了一系列以Co为主活性组分和碱土金属为助剂的CoM/RPSA（M=Mg、Ca、Sr和Ba）催化剂,考察了含硫和含氧条件下直接催化分解N2O的性能。采用X射线衍射、热重-质谱联用系统、NH3-TPD和N2O-TPD等方法对催化剂进行了表征。XRD结果表明,Co物种主要以Co3O4尖晶石形态存在。NH3-TPD和N2O-TPD结果表明,碱土金属的种类影响催化剂酸性和对反应物N2O的吸附-脱附性能,催化剂活性与催化剂酸性及其对反应物N2O的吸附-脱附性能有关。催化剂活性评价结果显示,CoSr/RPSA催化剂的N2O分解活性较好,N2O转化率达到95%时的反应温度为471 ℃。     

Formation of the rhodium oxides Rh2O3 and RhO2 in Rh/NaY

The oxidation states of Rh in NaY supported catalysts have been studied by temperature programmed reduction (TPR). After calcination of the exchanged catalyst to 380°C, both RhO₂ and Rh₂O₃ are identified, besides small amounts of RhO⁺ and Rh³⁺. Quantitative reduction is possible for samples calcined at temperatures not exceeding 500°C. Re-oxidation of the reduced samples leads to formation of RhO₂ and Rh₂O₃, with negligible protonolysis to Rh³⁺. The dioxide prevails after re-oxidation at 320°C, but the sesquioxide after oxidation at 500°C. In the temperature regime where both oxides coexist the reduction of NO with propane is catalyzed even at an O₂/C₃H₈ ratio of 10. Total oxidation of propane reaches 80% at 350°C.     

Co-production of hydrogen and multi-wall carbon nanotubes from ethanol decomposition over Fe/Al2O3 catalysts

The co-production of hydrogen and carbon nanotubes (CNTs) from the decomposition of ethanol over Fe/Al₂O₃ at different temperatures and feeding rates of ethanol was investigated systematically. The results indicated that Fe/Al₂O₃ was a quite active catalyst for the co-production of hydrogen and CNTs and that its activity and stability depended strongly on the Fe loading. Among all catalysts tested, 10 mol% Fe/Al₂O₃ was the most effective catalyst based on the ratio of hydrogen production, the total H₂ yield, and the quality of the CNTs formed. The efficiency of hydrogen production from ethanol decomposition over 10 mol% Fe/Al₂O₃ reached a maximum of ∼80% at 800 °C and the yield of CNTs with well-oriented growth and uniform diameter was 141%. In addition, the reaction of hydrogen and CNTs co-produced from ethanol decomposition was proposed.     

Benzene hydroisomerization over Pt/MOR/Al2O3 catalysts

Benzene hydroisomerization is among the promising processes converting benzene into methylcyclopentane (MCP), which is an environmentally friendlier, octane boosting component of motor fuels. Benzene hydroisomerization into MCP over the Pt/MOR/Al₂O₃ (MOR = mordenite) catalytic system is reported here. The dependence of the yield of the target product on the acidic properties of the support and platinum precursor ([Pt(NH₃)₄]Cl₂ or H₂PtCl₆) have been investigated in order to optimize the catalyst composition. The acidic properties of the surface have been altered by introducing 30–95 wt % alumina into the support. Catalytic activity has been measured in the hydroisomerization of cyclohexane and a benzene (20 wt %) + n-heptane (80 wt %) mixture in a flow reactor at 250–350°C, 1.5 MPa, H₂: CH = 3: 1, a cyclohexane LHSV of 6 h^?1, a mixed feedstock LHSV of 2 h^?1, a catalyst bed volume of 2 cm³, and catalyst pellet sizes of 0.25–0.75 mm. The most efficient catalyst for cyclohexane and n-heptane isomerization and benzene hydroisomerization is the platinum-containing catalyst (0.3 wt % Pt) whose support consists of 30 wt % MOR and 70 wt % Al2O3. The highest yield of the target products of isomerization in the presence of this catalyst is attained in the temperature range from 280 to 310°C, which is thermodynamically favorable for MCP formation from benzene. This indicates that this catalyst is promising for the hydroisomerization of benzene-containing gasoline fractions. Use of H₂PtCl₆, a readily available chemical, as the platinum precursor is favorable for commercialization of the catalyst and ensures price attractiveness in its industrial-scale manufacturing.     

Ag对Pd/Al2O3催化分解NO反应的促进作用

研究了不同含量的银对Pd/Al₂O₃催化分解NO反应活性的影响。结果表明，低温下，Pd/Al₂O₃催化剂对NO的分解反应活性不高；反应温度达到720 ℃时，NO分解活性迅速上升。O₂-TPD研究表明，Pd/Al₂O₃上氧的脱附速率也是在720 ℃左右达到最大值，因此，在温度低于720 ℃时，氧从催化剂表面的脱附是NO分解反应的速率控制步骤。Pd/Al₂O₃中添加适量的Ag对NO分解反应有促进作用。O₂-TPD研究表明，这种促进作用与Pd表面氧物种的起始脱附温度向低温移动有关。     

铑含量对Pt-Rh-Pd/Al2O3催化剂的氧化还原性能的影响

应用微反应装置研究了铑含量对Pt-Rh-Pd/Al2O3催化剂的催化活性以及吸附性能的影响.结果表明Rh含量在0%～0.015%之间时,催化剂对CO的活性曲线呈波浪形,对NO的活性曲线为增函数;当Rh含量超过0.015%时,增加Rh的量对CO和NO的转化率几乎无影响.在无助的情况下,用Al2O3为载体制作的Pt-Rh-Pd/Al2O3催化剂,其Pt、Rh、Pd之间的最佳比例为15320.Rh含量的增加有利于氧化性气体的吸附,不利于还原性气体的吸附.