Al2O3-supported transition-metal oxide catalysts for catalytic incineration of toluene

The catalytic incineration of toluene over gamma-Al2O3-supported transition-metal oxide catalysts in the temperature range of 200-380 degrees C was investigated employing a fixed bed flow reactor. CuO/gamma-Al2O3 was found to be the most active of seven catalysts tested. Using this catalyst with different wt% Cu in the incineration of toluene, we found that the optimal Cu content was 5 wt%. X-ray diffraction, BET surface area and hydrogen-temperature-programmed reduction showed that it was mainly the formation of large CuO crystals that caused declines in catalyst activity at Cu content above 5 wt%. Addition of water vapor or CO2 inhibited catalyst activity, but this effect was reversible. Although coexistence of toluene and n-hexane resulted in a reduction in n-hexane conversion, the impact on toluene oxidation was only negligible. Temperature-programmed desorption revealed that this differential effect was due to more competitive adsorption of toluene onto active sites of the catalyst.     

The utilization of catalyst sorbent in scrubbing acid gases from incineration flue gas

Catalyst sorbents based on alumina-supported CuO, CeO2, and CuO-CeO2 were applied to a dry scrubber to clean up the SO2/HCl/NO simultaneously from pilot-scale fluidized-bed incineration flue gas. In the presence of organic compounds, CO and the submicron particles SO2 and HCI removed by the fresh catalyst sorbents and NO reduced to N2 by NH3 under the catalysis of fresh and spent desulfurization/dechloridization (DeSO2/DeHCl) catalyst sorbents (copper compounds, Cu, CuO, and CuSO4) were evaluated in this paper. The fresh and spent catalyst sorbents were characterized by the Brunner-Emmett-Teller method (BET), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), inductively coupled plasma-mass spectrometry (ICP-MS), and the elemental analyzer (EA). The study showed that the performances of CuO, CeO2, and CuO-CeO2/gamma-Al2O3 were better than that of Ca(OH)2. The removal efficiency of SO2 and HCl was 80-95% in the dry scrubber system. Under NH3/NO = 1, NO could not be reduced to N2 because it was difficult to control the ratio of air/fuel in the flue gas. For estimating the feasibility of regenerating the spent catalyst sorbents, BET and EA analyses were used. They indicated that the pore structures were nearly maintained and a small amount of carbon accumulated on their surface.     

CWAO of phenol using CeO2/gamma-Al2O3 with promoter--effectiveness of promoter addition and catalyst regeneration

The effect of promoter addition on activity of CeO(2)/gamma-Al(2)O(3) was assessed via the CWAO of phenol. Adding Cu as the promoter rendered the most effective performance, followed by Mn, although the performance of Mn-promoted catalyst was inferior to CeO(2)/gamma-Al(2)O(3). Mineralization of phenol was effectively implemented at 160 degrees C using Cu-promoted catalyst (Ce15Cu5). Furthermore, at 180 degrees C this catalyst produced about 100% conversion of phenol (1h) and 95% removal of chemical oxygen demand (4h), higher than that of CeO(2)/gamma-Al(2)O(3). In contrast, Mn-promoted catalyst (Ce15Mn5) required a temperature above 220 degrees C for acceptable performance. Activity of re-used catalyst declined noticeably, due to deposits of carbonaceous compounds and leaching of metal ions. Regeneration with acetone rinsing after the first run was effective in recovering activity of Ce15Cu5, although after a second run further regeneration with acetone rinsing had only a moderate effect, due to residual carbonaceous deposits and the additive effect of leached metal species in each run. As an alternative to acetone, HCl or HNO(3) solution (0.01 M) was less effective at regenerating activity. In promoted catalysts, leached metal ions accounted for the majority of mineralization of phenol, while the solid catalyst played a dual role of initiator and terminator of free radicals. Despite a superior catalytic performance, leaching of Cu(2+) from the promoted catalyst caused a severe decline in activity and poses the problem of secondary pollution of treated wastewater. Therefore, addition of Cu, as well as other metal species, is unfavorable in promoting the CeO(2)/gamma-Al(2)O(3) catalyst.     

The promoter effect and a rate expression of the catalytic incineration of (CH3)2S2 over an improved CuO-MoO3/gamma-Al2O3 catalyst

The CuO-MoO3/gamma-Al2O3 catalyst, confirmed previously as having good activity in the catalytic incineration of (CH3)2S2, was employed as the principal catalyst in this study. With the aim of improving catalyst activity and resistance to deactivation by sulfur compounds, a promoter was added either before adding the precursors of Cu and Mo or together with Cu and Mo onto the gamma-Al2O3. Promoters included transition metals and elements from groups IA-VIIA in the chemical periodic table. Experimental results reveal Cr2O3 as the most effective promoter, with an optimal composition of 5 wt.% Cu, 6 wt.% Mo and 4 wt.% Cr (designated as Cu(5)-Mo(6)-Cr(4)/gamma-Al2O3). Knowing that higher acidity can improve activity, we further investigated the effect of acid treatment on the performance of the Cu(5)-Mo(6)-Cr(4)/gamma-Al2O3 catalyst. Experimental results indicate the H2SO4-treated catalyst (Cu(5)-Mo(6)-Cr(4)/sulfated-gamma-Al2O3) has a better activity and durability. A study for finding an appropriate rate expression for the catalytic incineration of (CH3)2S2 by Cu(5)-Mo(6)-Cr(4)/sulfated-gamma-Al2O3 was carried out in a differential reactor. The results show that the Mars-Van Krevelen model is applicable to this destructive oxidation reaction. Results additionally reveal that competitive adsorption of CH4 reduces conversion of (CH3)2S2.     

CuO（-CeO2）/SBA-15对萘氧化的催化活性及CO2选择性研究

通过浸渍法制备CuO/SBA-15和CuO-CeO2/SBA-15两种介孔材料催化剂,采用BET、XRD、TPR和XPS等对催化剂进行表征,重点考察催化剂对萘氧化反应的催化活性及对产物CO2的选择性。BET、XRD和XPS等实验结果表明CuO高度分散于介孔分子筛SBA-15中,CeO2可促进CuO在载体上的分散,同时能降低催化剂的TPR还原温度。活性测试结果表明CuO/SBA-15对萘氧化反应的催化活性较高,但是催化氧化的CO2选择性较低,温度在380℃时CO2的生成率仅为60%左右;CeO2的添加不仅提高了CO2的生成率,15%CuO-15%CeO2/SBA-15在325℃使CO2生成率达到99%,而且CeO2增强了催化剂的稳定性。     

Supported transition-metal oxide catalysts for reduction of sulfur dioxide with hydrogen to elemental sulfur

This work is for the purpose to find a high performance catalyst for the catalytic reduction of SO2 with H2 as a reducing agent. NiO/gamma-Al2O3 catalyst was found to be the most active catalyst among the seven gamma-Al2O3-supported metal-oxide catalysts tested. With NiO as the active species, of the supports tested, gamma-Al2O3 was the most suitable one and the optimal Ni content was 16 wt%. Using this NiO/gamma-Al2O3 catalyst, we found that the optimal feed ratio of H2/SO2 is 2:1 and the catalyst presulfided with H2 + H2S exhibits a higher performance than that pretreated with H2 or He. XRD patterns reveal that the nickel oxide experienced a transformation to Ni3S2 and NiS, and then to NiS2, the most active nickel sulfide, during the reaction process. The reason for the highest catalyst activity of 16 wt% Ni was attributed to the largest amount of NiS2. Water vapor in the feed gas reactant caused inhibition of catalyst activity, whereas H2S promoted the reduction of SO2. These phenomena were rationalized with the aid of Claus reaction.     

An assessment of the suitable operating conditions for the CeO2/gamma-Al2O3 catalyzed wet air oxidation of phenol

It has been shown that the CeO2/gamma-Al2O3 catalyst is a feasible alternative to CeO2 for the catalytic wet air oxidation (CWAO) of phenol because it remains an effective catalyst and yet is cheaper to prepare. In this study, we found that the optimal cerium content in the CeO2/gamma-Al2O3 catalyst was 20 wt.%, regardless of catalyst loading. Furthermore, at 180 degrees C, with a phenol concentration of 1000 mg l(-1), and an O2 partial pressure of 1.0M Pa or 1.5M Pa, the optimal catalyst loading was 3.0 gl (-1). The efficacy of CWAO of phenol improved with O2 partial pressure, although the effects of O2 pressure were more significant between 0.5 MPa and 1.5 MPa than between 1.5 MPa and 2.0 MPa. After 2 h of reaction, approximately 100% phenol conversion and 80% total organic carbon (TOC) removal was recorded at 180 degrees C, 1000 mg l(-1) of phenol and 3.0 g l(-1) of catalyst. Because these percentages subsequently leveled off, it is suggested that 2 h is a suitable time over which to run the reaction. The efficacy of CWAO of phenol decreased as initial phenol concentration was raised (from 400 to 2500 mg l(-1)), with the exception of phenol conversion after about 2 h, for which 400 mg l(-1) produced the lowest phenol conversion figure. Higher phenol concentrations require both catalyst loading and O2 partial pressure to be increased to maintain high performance. For example, for 2000 mg l(-1) and 2500 mg l(-1) phenol, nearly 100% phenol conversion and 90% TOC removal after 4 h of reaction at 180 degrees C required 4.0 g l(-1) of catalyst and 2.0 MPa.     

Incinerating volatile organic compounds with ferrospinel catalyst MnFe2O4: an example with isopropyl alcohol

This paper concerns the incineration of isopropyl alcohol (IPA) using the ferrospinel catalyst MnFe2O4. It covers the preparation of the ferrospinel catalyst, the screening of catalytic activity, catalytic incineration testing, and 72-hr decay testing of the catalyst. The experimental results of catalyst screening reveal that the Mn/Fe catalyst is the best of five prepared catalysts (chromium/iron [Cr/Fe], manganese/iron [Mn/Fe], zinc/iron [Zn/Fe], nickel/iron [Ni/Fe], and pure magnetite [Fe3O4]). In tests of the catalytic incineration system used to convert IPA, 98% conversion was obtained at a space velocity of 24,000 hr(-1), an oxygen (O2) content of 21%, 1700 ppm of IPA, and a reaction temperature of 200 degrees C.     

Noble metal catalysts for methane removal

Using a bench-scale rig, the activities of Pt, Pd and Pt+Pd catalysts supported on gamma-Al(2)O(3) and on TiO(2) (anatase) for the complete oxidation of methane (300 ppmv) in air have been measured as a function of temperature; values of T(10), T(50) and T(90) together with the Arrhenius parameters (activation energy and pre-exponential factor) are reported. Pt is less active than Pd when deposited on the surface of the TiO(2), but more active when deposited on gamma-Al(2)O(3), however when combined, the Pt+Pd mixture is more active than either metal individually. The T(10) for Pt+Pd/gamma-Al(2)O(3) was being as low as 228 degrees C. The significance of the Arrhenius parameters, for metal containing catalysts is that they exhibit compensation with increasing activation energy, while securing a more rapid increase in conversion from 0% to 100% when the temperature is increased.     

Surface properties and catalytic performance of La(1-x)Sr(x)FeO(3) perovskite-type oxides for methane combustion

La(1-x)Sr(x)FeO(3) (x=0.0-1.0) perovskites were prepared and tested for the combustion of methane. X-ray diffraction (XRD) patterns revealed the presence of a single perovskite structure for substitutions 0x0.3, however Fe(2)O(3), SrCO(3) and SrFeO(3) phases were observed for substitutions x>0.3. The results of activity test indicate that with La(1-x)Sr(x)FeO(3) as the catalyst, the combustion of methane can take place at low temperatures around 400 degrees C. Partial substitution of La with Sr increases the activity and an optimal substitution fraction (x=0.5) exists in the La(1-x)Sr(x)FeO(3) catalysts. Catalyst activity can be well correlated to the product of the specific surface area and atomic ratio of Fe to La+Sr on the catalyst surface. Experimental results of O(2)-TPD and CH(4)-TPD in the range of 350-500 degrees C indicate that the amount of oxygen desorbed from the La(1-x)Sr(x)FeO(3) catalysts is far larger than that of methane. Therefore, it can be proposed that the catalytic oxidation of CH(4) over these catalysts proceeds with the surface reaction between CH(4) in the gas phase and the adsorbed O(2). Addition of water vapor or CO(2) to the feed inhibited catalyst activity, but the inhibition was reversible and became negligible at high reaction temperature.     

Mn的氧化价态对Mn／γ-Al2O3催化剂催化臭氧氧化气相低浓度甲苯的影响

采用共沉淀法,以Al2O3为载体制备Mn／γ-Al2O3和Mn—Ce／Mn／γ-Al2O3催化剂,并分别在N2气氛和O2气氛下焙烧。采用固定床连续流动反应器,研究所制备催化剂在室温条件下催化臭氧氧化甲苯的性能。通过XRD、XPS和FTIR等手段对催化剂的结构和组成进行表征。结果表明,Mn／Mn／γ-Al2O3催化剂具有良好的催化臭氧氧化甲苯和催化臭氧自身分解的性能,共沉淀法制备催化剂的最佳Mn负载量为20％。O2气氛焙烧和Ce的加入,可以有效提高催化剂的活性和寿命。原因是O2气氛焙烧和Ce的加入可以提高Mn的氧化价态。催化剂失活的主要原因是有机副产物在催化剂表面吸附堆积,失活催化剂在550℃、空气气氛下焙烧可恢复催化性能。     

Investigation of the generation of hydroxyl radicals and their oxidative role in the presence of heterogeneous copper catalysts

The presence and impact of hydroxyl radicals generated via the catalytic decomposition of H(2)O(2) over heterogeneous copper catalysts were investigated by using two detection methods, an electron spin resonance-spin trapping method and a chemical probe method. Detection of the (5,5-dimethyl-1-pyrroline-N-oxide)-OH adduct signal and formation of 4-chlorocatechol during the oxidation of a 4-chlorophenol substrate demonstrated that the three heterogeneous copper catalysts employed here (CuO, Cu/Al(2)O(3) and CuO.ZnO/Al(2)O(3)) were capable of generating hydroxyl radicals in combination with H(2)O(2). The oxidative mechanism of the hydroxyl radical in the presence of heterogeneous copper catalysts is discussed with regard to the further oxidation of the (5,5-dimethyl-1-pyrroline-N-oxide)-OH adduct and hydroxylated products of 4-chlorophenol oxidation. Interestingly, integration of the 5,5-dimethyl-1-pyrroline-N-oxide-OH adduct signal could not be used to reliably measure the total amount of hydroxyl radicals generated as a result of oxidative attack on the adduct. This may be as a result of locally higher hydroxyl radical concentrations in the presence of a heterogeneous catalyst leading to further unwanted oxidation of the (5,5-dimethyl-1-pyrroline-N-oxide)-OH.     

Catalytic wet oxidation of the pretreated synthetic pulp and paper mill effluent under moderate conditions

In the present study, catalytic wet oxidation (CWO) was investigated for the destruction of organic pollutants in the thermally pretreated effluent from a pulp and paper mill under moderate temperature and pressure conditions. The thermal pretreatment studies were conducted at atmospheric pressure and 368K using copper sulfate as a catalyst. The thermal pretreatment reduced COD by about 61%. The filtrate of the thermal pretreatment step was used at pH 8.0 for CWO at 383-443K temperature and a total pressure of 0.85MPa for 4h. Catalysts used for the reaction include copper sulfate, 5% CuO/95% activated carbon, 60% CuO/40% MnO(2), and 60% CuO/40% CeO(2). Maximum COD reduction was found to be 89% during CWO step using 5% CuO/95% activated carbon with a catalyst loading of 8gl(-1) at 443K and 0.85MPa total pressure. Overall COD reduction for the pretreatment and the CWO was found to be 96%. Besides this, 60% CuO/40% CeO(2) catalyst also exhibited the similar activity as that of obtained with 5% CuO/95% activated carbon catalyst at 423K temperature and 0.85MPa total pressure. The pH of the solution during the experimental runs decreases initially due to the formation of carboxylic acid and then increases due to the decomposition of acids.     

Kinetics of catalytic oxidation of benzene, n-hexane, and emission gas from a refinery oil/water separator over a chromium oxide catalyst

With the advances made in the past decade, catalytic incineration of volatile organic compounds (VOCs) has become the technology of choice in a wide range of pollution abatement strategies. In this study, a test was undertaken for the catalytic incineration, over a chromium oxide (Cr2O3) catalyst, of n-hexane, benzene, and an emission air/vapor mixture collected from an oil/water separator of a refinery. Reactions were carried out by controlling the feed stream to constant VOC concentrations and temperatures, in the ranges of 1300-14,700 mg/m3 and 240-400 degrees C, respectively. The destruction efficiency for each of the three VOCs as a function of influent gas temperature and empty bed gas residence time was obtained. Results indicate that n-hexane and the oil vapor with a composition of straight- and branch-chain aliphatic hydrocarbons exhibited similar catalytic incineration effects, while benzene required a higher incineration temperature or longer gas retention time to achieve comparable results. In the range of the VOC concentrations studied, at a given gas residence time, increasing the operating temperature of the catalyst bed increased the destruction efficiency. However, the much higher temperatures required for a destruction efficiency of over 99% may be not cost-effective and are not suggested. A first-order kinetics with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant appeared to be an adequate representation for the catalytic oxidation of these volatile organics. Activation energy and kinetic constants were estimated for each of the VOCs. Low-temperature destruction of the target volatile organics could be achieved by using the Cr2O3 catalyst.     

双氧水催化氧化中Cu/γ-Al_2O_3催化剂的稳定性研究

针对废水湿式双氧水催化氧化,采用浸渍法制备Cu催化剂,研究非均相Cu催化剂在常温常压湿式双氧水催化氧化中的稳定性与失活问题。研究表明,催化剂制备条件及催化氧化反应条件对催化剂中Cu2＋溶出均有影响。研究同时表明,催化剂失活与活性组分流失和活性组分被有机中间产物覆盖有关,高温焙烧可对催化剂再生。     

Ti-Ce-Zr-Ox复合脱硝催化剂的制备及其性能研究

采用共混法制备了Ti-Ce-Zr-Ox复合脱硝催化剂TiCe0.1Zr0.1O2.4,运用X射线衍射、氮气物理吸附、扫描电镜等表征手段,分别对该催化剂的晶型、表面积、孔分布及结构形貌进行了分析,同时考察了反应温度、空速、水蒸气和SO2对该催化剂NH3选择性催化还原NO的影响.结果表明,TiCe0.1Zr0.1O2.4催...     

The characteristics of wet air oxidation of phenol over CuOx/Al2O3 catalysts: effect of copper loading

The nature of active copper species is well-known to vary with copper loading, i.e., isolated Cu(2+) to bulk CuO. In this work, however, the effect of copper loading on the activity and the selectivity was investigated for the wet oxidation of phenol over CuO(x)/Al(2)O(3) catalysts. The activity and the mineralization selectivity of the catalysts increased with copper loading up to 7wt% and remained almost the same at a higher loading. The optimum copper loading was about 7wt% for the wet oxidation of phenol over CuO(x)/Al(2)O(3) catalysts in this work. The nature of copper species with different loading was characterized with TPR, XRD, and XANES. The chemical states of copper in the CuO(x)/Al(2)O(3) catalysts were confirmed as varying with copper loading: isolated Cu(2+) ions for 1wt%; highly dispersed Cu(2+) cluster for 5wt% and 7wt%, and bulk CuO for 10-25wt%. The stability of the CuO(x)/Al(2)O(3) catalysts with different copper loading was also studied with respect to carbonaceous deposits and copper leaching.     

Superior pillared clay catalysts for selective catalytic reduction of nitrogen oxides for power plant emission control

Fe(3+)-, Cr(3+)-, Cu(2+)-, Mn(2+)-, Co(2+)-, and Ni(2+)-exchanged Al2O3-pillared interlayer clay (PILC) or TiO2-PILC catalysts are investigated for the selective catalytic reduction (SCR) of nitric oxide by ammonia in the presence of excess oxygen. Fe(3+)-exchanged pillared clay is found to be the most active. The catalytic activity of Fe-TiO2-PILC could be further improved by the addition of a small amount of cerium ions or cerium oxide. H2O and SO2 increase both the activity and the product selectivity to N2. The maximum activity on the Ce-Fe-TiO2-PILC is more than 3 times as active as that on a vanadium catalyst. Moreover, compared to the V2O5-WO3/TiO2 catalyst, the Fe-TiO2-PILC catalysts show higher N2/N2O product selectivities and substantially lower activities (by approximately 85%) for SO2 oxidation to SO3 under the same reaction conditions. A 100-hr run in the presence of H2O and SO2 for the CeO2/Fe-TiO2-PILC catalyst showed no decrease in activity.     

ACF负载复合金属氧化物催化还原NO的研究

为了研究活性碳纤维（ACF）负载复合金属氧化物催化还原NO的效果,采用浸渍法制备了系列负载氧化铈和氧化铜的ACF,在微型反应器中进行程序升温反应,通过正交试验,确定催化反应的最佳条件,考察了反应温度和复合金属氧化物的不同含量对催化活性的影响,并与ACF负载单金属氧化物作了比较,同时对催化剂进行了扫描电镜和傅里叶红外光谱分析实验。实验结果表明,在氨氮比是1.1∶1,氧气体积比为5%,体积流速为4 000 h^-1的条件下,负载复合金属氧化物的ACF低温活性相差很大,随着温度的升高,催化效率持续提高。当氧化铈与氧化铜的含量分别为10%和30%,在120～300℃区域内去除率维持80%以上,是低温催化中理想的催化剂。     

Catalytic oxidation of organic compounds in incineration flue gas by a commercial palladium catalyst

The object of this study is to investigate the effect of different operation conditions on the catalytic oxidation of trace organic compounds [i.e., benzene, toluene, ethylbenzene, and xylene (BTEX); and polyaromatic hydrocarbons (PAHs)] in incineration flue gas. A commercial Pd-based honeycomb catalyst, which is applied to treat flue gas with low organic concentrations and high gas velocity, is employed in this study. The investigated parameters include (1) effect of different space velocities, (2) effect of heavy metals, (3) effect of acid gas, and (4) effect of water vapor and ash particles. In this work, an effective catalyst oxidation system is constructed and expected to purify the incineration flue gas. Catalyst oxidation is a potential purification system that will meet the stricter regulations on the emissions of incineration systems. Experimental results showed that the destruction efficiency of PAHs and BTEX in Pd catalyst was generally greater than 80%. Decreasing the space velocity increased the decomposition efficiency of organic compounds. When the feedstock contained the heavy metals Pb and Cr, the oxidation of organic compounds was not inhibited. But the presence of Cd significantly decreased the oxidation efficiency. The acid gases SO2 and HCl in the flue gas could have influenced the crystal structure of PdO and subsequently deactivated/poisoned the Pd catalyst. The effect of water vapor on the catalytic destruction of PAHs and BTEX was not obvious.