Modeling adsorption in multicomponent systems using a Freundlich-type isotherm

The suitability of a Freundlich-type isotherm, the Sheindorf-Rebuhn-Sheintuch (SRS) equation, to represent the competitive adsorption of Sr, Cs and Co in Ca-montmorillonite suspensions was investigated. Experimental adsorption data were obtained for systems containing these cations as single-component, binary and ternary mixtures. The competition coefficient α_ij, which were obtained based on the experimental adsorption data for bicomponent systems, can be viewed as a way to quantify competitive interactions. The competition coefficients obtained for the cations under consideration indicate that their competitive interactions are of similar magnitude, with the cation least affected by competitive effects being Cs, while the adsorption of Co was more significantly affected by the presence of Cs, and Sr by the presence of Co. After α_ij-values were substituted in the SRS equation, the adsorption of systems of three or more components could be predicted. To validate the SRS equation, the adsorption values predicted by this equation for the ternary mixture Sr---Cs--- Co were compared to values determined experimentally. The SRS equation successfully modeled adsorption for the range of concentrations that followed Freundlich behavior.     

Geochemistry of inorganic arsenic and selenium in a tropical soil: effect of reaction time, pH, and competitive anions on arsenic and selenium adsorption

Factors that can affect As and Se adsorption by soils influence the bioavailability and mobility of these elements in the subsurface. This research attempted to compare the adsorption capacities of As(III), As(V), Se(IV), and Se(VI) on a tropical soil commonly found in Singapore in a single-species system. The effect of reaction time, pH, and competitive anions at different concentrations on the adsorption of both As and Se species were investigated. The As and Se adsorption isotherm were also obtained under different background electrolytes. The batch adsorption experiments showed that the sequence of the As and Se adsorption capacities in the soil was As(V) > Se(IV) > As(III) > Se(VI). The adsorption kinetics could be best described by the Elovich equation. The adsorption of As(V), Se(IV), and Se(VI) appeared to be influenced by the variable pH-dependent charges developed on the soil particle surfaces. Phosphate had more profound effect than SO4(2-) on As and Se adsorption in the soil. The competition between PO4(3-) and As or Se oxyanions on adsorption sites was presumably due to the formation of surface complexes and the surface accumulation or precipitation involving PO4(3-). The thermodynamic adsorption data for As(V) and Se(IV) adsorption followed the Langmuir equation, while the As(III) and Se(VI) adsorption data appeared to be best-represented by the Freundlich equation.     

Modeling the competitive effect of phosphate, sulfate, silicate, and tungstate anions on the adsorption of molybdate onto goethite

The mobility of Mo in soils and sediments depends on several factors including soil mineralogy and the presence of other oxyanions that compete with Mo for the adsorbent's retention sites. Batch experiments addressing Mo adsorption onto goethite were conducted with phosphate, sulfate, silicate, and tungstate as competing anions in order to produce competitive two anions adsorption envelopes, as well as competitive two anions adsorption isotherms. Tungstate and phosphate appear to be the strongest competitors of Mo for the adsorption sites of goethite, whereas little competitive effects were observed in the case of silicate and sulfate. Mo adsorption isotherm from a phosphate solution was similar to the one from a tungstate solution. The charge distribution multi-site complexation (CD-MUSIC) model was used to predict competitive adsorption between MoO(4)(2-) and other anions (i.e., phosphate, sulfate, silicate and tungstate) using model parameters obtained from the fitting of single ion adsorption envelopes. CD-MUSIC results strongly agree with the experimental adsorption envelopes of molybdate over the pH range from 3.5 to 10. Furthermore, CD-MUSIC prediction of the molybdate adsorption isotherm show a satisfactory fit of the experimental results. Modeling results suggest that the diprotonated monodentate complexes, FeOW(OH)(5)(-0.5) and FeOMo(OH)(5)(-0.5), were respectively the dominant complexes of adsorbed W and Mo on goethite 110 faces at low pH. The model suggests that Mo and W are retained mainly by the formation of monodentate complexes on the goethite surface. Our results indicate that surface complexation modeling may have applications in predicting competitive adsorption in more complex systems containing multiple competing ions.     

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.     

Adsorption of molybdate and tetrathiomolybdate onto pyrite and goethite: effect of pH and competitive anions

The adsorption of two major molybdenum (Mo) species, molybdate (MoO4(2-)) and tetrathiomolybdate (MoS4(2-)) onto two main iron minerals pyrite (FeS2) and goethite (FeOOH) is addressed to elucidate the possible mechanisms of molybdenum immobilization in anoxic sediments. Suspensions of MoS4(2-) (or MoO4(2-)) and goethite (or pyrite) in 0.1M NaCl solution were equilibrated under anoxic conditions at 25 degrees C in the pH range from 3 to 10. The competitive effects of sulfate, phosphate, and silicate on the adsorption of MoO4(2-) and MoS4(2-) by pyrite and goethite are also addressed. Adsorption of MoO4(2-) and MoS4(2-) on pyrite and goethite is in general well described by a Langmuir model at low pH; the extent of sorption is a function of pH and the surface loading. Maximum sorption is observed in the acidic pH range (pH<5) at low surface loading. The adsorption of molybdenum (micromol g(-1)) depends upon Mo species and on the type of iron mineral following the order: MoS4(2-)-goethite > MoO4(2-)-goethite > MoS4(2-)-pyrite > MoO4(2-)-pyrite. Phosphate appears to compete strongly with MoO4(2-) and MoS4(2-) for the sorption sites of pyrite and goethite. The strength of the phosphate competitive effect follows the sequence of MoO4(2-)-goethite approximately = MoO4(2-)-pyrite > MoS4(2-)-pyrite > MoS4(2-)-goethite. Silicate and sulfate have a negligible effect on the sorption of MoO4(2-) and MoS4(2-). The preferred adsorption by iron mineral of MoS4(2-), as well as its behavior in the presence of competitive anions suggests that tetrathiomolybdate species may be an ultimate reservoir and may control Mo enrichment in the sediments.     

Evaluation of the multiple-ion competition in the adsorption of As(V) onto reclaimed iron-oxide coated sands by fractional factorial design

This study describes the competitive effects of selected ions and natural organic matter on As(V) removal using reclaimed iron-oxide coated sands (RIOCS) in the single- and multi-ion systems. A 2(7-3) factional factorial experimental design (FFD) was employed for screening main competitive factors in this adsorption process. As a result, the inhibitive competition effects of the anions on As(V) removal in the single ion system were in the following sequence: PO(4)(3-)>SiO(3)(2-)>HCO(3)(-)>humic acid (HA)>SO(4)(2-)>Cl(-), whereas the cation Ca(2+) was observed to enhance the As(V) removal. In addition, the optimum initial pH for As(V) removal in single-ion system was 5. Based on the estimates of major effects and interactions from the FFD, PO(4)(3-), SiO(3)(2-), Ca(2+) and HA were important factors on As(V) removal in the multi-ion system. The promoters for the As(V) removal were found to be Ca(2+) and, to a lesser extent, SO(4)(2-). The competitive effects of these ions on As(V) removal were in the order of PO(4)(3-), SiO(3)(2-), HA, HCO(3)(-), and Cl(-). In the single ion system, the efficiencies of As(V) removal range from 75% to 96%, much higher than those in the multi-ion system (44%) at the initial pH 5. Clearly, there were some complex anion interactions in the multi-ion system. To promote the removal of As(V) by RIOCS, it is proposed to lower the pH in the single-ion system, while in the multi-ion system, the increase of the Ca(2+) concentration, or decreases of PO(4)(3-), SiO(3)(2-) and HA concentrations is suggested.     

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.     

Enhancement of copper and cadmium adsorption on kaolin by the presence of humic acids

The competitive adsorption equilibrium isotherms of Cu²⁺ and Cd²⁺ on kaolin have been measured at 298 K, in the presence and the absence of humic acids (HAs). HAs were found to enhance the metal adsorption capacity of mineral surfaces, in particular kaolin. This enhancement was also observed in the competitive adsorption of copper and cadmium on kaolin and kaolin–HA complex. This competitive adsorption shows that the presence of Cd²⁺ has not an important effect on Cu²⁺ adsorption, whereas a dramatic decrease is observed on the adsorption of Cd²⁺ in the presence of Cu²⁺. The Freundlich isotherm equation was found to provide an excellent fit to the experimental data. These results were compared with the independent adsorption of both heavy metals.     

Effects of dissolved oxygen, pH, and anions on the 2,3-dichlorophenol degradation by photocatalytic reaction with anodic TiO(2) nanotube films

In this study, the highly-ordered TiO(2) nanotube (TNT) arrays on titanium sheets were prepared by an anodic oxidation method. Under UV illumination, the TNT films demonstrated the higher photocatalytic activity in terms of 2,3-dichlorophenol (2,3-DCP) degradation in aqueous solution than the conventional TiO(2) thin films prepared by a sol-gel method. The effects of dissolved oxygen (DO) and pH on the photocatalytic degradation of 2,3-DCP were investigated. The results showed that the role of DO in the 2,3-DCP degradation with the TNT film was significant. It was found that 2,3-DCP in alkaline solution was degraded and dechlorinated faster than that in acidic solution whereas dissolved organic carbon removal presented an opposite order in dependence of pH. In the meantime, some main intermediate products from 2,3-DCP degradation were identified by a (1)H NMR technique to explore a possible degradation pathway. A major intermediate, 2-chlororesorcinol, was identified from the 2,3-DCP decomposition as a new species compared to the findings in previous reports. Photocatalytic deactivation was also evaluated in the presence of individual anions (NO(3)(-), Cl(-), SO(4)(2-), and H(2)PO(4)(-)). The inhibition degree of photocatalytic degradation of 2,3-DCP caused by these anions can be ranked from high to low as SO(4)(2-)>Cl(-)>H(2)PO(4)(-)>NO(3)(-). The observed inhibition effect can be attributed to the competitive adsorption and the formation of less reactive radicals during the photocatalytic reaction.     

Temporal variation in daily concentrations of ozone and acid-related substances at Saturna Island, British Columbia

A multiple linear regression model was used to investigate seasonal and long-term trends in concentrations of ozone (O3) and acid-related substances at the Saturna Island monitoring station in southwestern British Columbia from 1991 to 2000. Statistically significant primary (dominant) cycles with a period of 1 yr were found for O3, sulfur dioxide (SO2), nitric acid (HNO3), and aerosol concentrations of sulfate (SO4(2-)), calcium (Ca2+) and chloride (Cl-). Of these, peak median concentrations occurred during the spring for O3 and Ca2+, during the warmer, drier months (April-September) for SO4(2-) and HNO3, and during the cooler, wetter months (October-March) for SO2 and Cl-. Statistically significant secondary cycles of 6 months duration were seen for concentrations of O3, SO4(2-), HNO3, Ca2+, and Cl-. Daily maximum O3 concentrations exhibited a statistically significant increase over the period of record of 0.33 +/- 0.26 ppb/yr. Statistically significant declines were found for concentrations of SO2, SO4(2-), HNO3, Ca2+, and potassium, ranging from 20 to 36% from levels at the start of the sampling period. Declines in ambient concentrations of SO2, SO4(2-), and HNO3 reflect local declines in anthropogenic emissions of the primary precursors SO2 and NOx over the past decade. Trends in Ca2+ and potassium ion concentrations are in line with a broader North American declining trend in acid-neutralizing cations.     

Composition of wet and bulk deposition in Erzurum, Turkey

Seasonal variations in the chemical characteristics of wet and bulk deposition samples collected in Erzurum were investigated for the period March 2002-January 2003. Major cations (Ca2+, K+, Mg2+) and major anions (SO4(2-),NO3-) were determined in bulk and wet deposition samples; pH was also measured in wet deposition. The average pH of the wet deposition at Erzurum was 6.6 due to extensive neutralization of the acidity. A strong relationship between pH and SO4(2-) concentrations was observed in all seasons; however, only a weak relationship was found between pH and NO3-. On a seasonal basis, the correlation between Ca2+ and SO4(2-) concentrations was stronger in winter than in summer. Seasonal variations of ions were examined in both wet and bulk deposition samples. Although maximum concentrations of anions generally occurred during winter and spring, cation concentrations peaked in summer for both wet and bulk deposition. Results indicated that Ca2+ was the dominant cation and SO4(2-) the dominant anion in all deposition samples at Erzurum. Even though correlations among the crustal ions (calcium, magnesium and potassium) were high, the relationship between anthropogenic ions (sulfate and nitrate) was less clear in bulk deposition.     

大洋锰结核在环境污染治理方面的应用

大洋锰结核能够有效分解转化气体污染物(如CO、CH、VOC、NOx、SO2);能够吸附水体中的Cu、CO、Ni、Mn、Zn、Cr、Hg、Pb、As等重金属阳离子和PO4^3-、SeO3^2-等阴离子;可做生物固定化载体除去水体中的有机污染物。大洋锰结核具有良好的环境矿物学属性,是一种理想的环境矿物材料,为环境治理提供了新的方向。     

Arsenic(V) removal with a Ce(IV)-doped iron oxide adsorbent

The removal of arsenic(V) by a new Ce-Fe adsorbent was evaluated under various conditions. Under an initial As(V) of 1.0 mg l(-1), the adsorption capacity of the Ce-Fe absorbent was constant around a value of 16 mgg(-1) over a wide pH range (3-7), while a maximum adsorption capacity of 8.3 mgg(-1) was obtained over a narrow pH range around 5.5 for activated alumina, a conventional adsorbent. Kinetics of adsorption obeys a pseudo-first-order rate equation with the rate constant K(ad) as 1.84 x 10(-3) min(-1). The pattern of adsorption of As(V) by the adsorbent fitted well both the Langmuir and Freundlich models. A Langmuir Q(0) of 70.4 mgg(-1) was obtained at an initial pH of 5.0 and temperature of 20 degrees C, significantly higher than those of other adsorbents reported. Phosphate seriously inhibited the removal of As(V) while fluoride did not compete with As(V) even at an F/As molar ratio as high as 30, suggesting that the adsorption sites for As(V) and fluoride were different. Salinity, hardness, and other inorganic anions such as Cl(-), NO(3)(-), and SO(4)(2-) had no apparent effect on As(V) adsorption. Fourier transform infrared spectra of Ce-Fe adsorbent before and after As(V) adsorption demonstrated that M-OH groups plays an important role for As(V) ions removal in the adsorption mechanisms of Ce-Fe adsorbent.     

磷酸根和硫离子在纳米铁表面的竞争吸附

通过纳米铁对磷酸根和硫离子的单吸附和竞争吸附的研究,从吸附动力学和吸附等温线两个方面分析并验证了其吸附特性和模式。分析表明,相对于磷酸根,纳米铁对硫离子的吸附能力更强,在竞争条件下居优势地位。采用准一级和准二级吸附动力学方程对实验数据进行模拟分析,结果表明,纳米铁对磷酸根和硫离子的吸附符合二级动力学方程。吸附等温线分析采用Freundlich和Langmuir吸附等温线方程模拟分析,分析结果表明,纳米铁颗粒对磷酸根的吸附符合Freundlich吸附模式,而对硫离子的吸附符合Langmuir吸附模式。     

Summer-time distribution of air pollutants in Sequoia National Park, California

Concentrations of air pollutants were monitored during the May November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3-), ammonium (NH4+), and sulfate (SO4(2-)); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41-71 ppb), HNO3 (seasonal means 0.4-2.9 microg/m3), NH3 (seasonal means 1.6-4.5 microg/m3), NO3 (1.1-2.0 microg/m3) and NH4+ (1.0-1.9 microg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park.     

Predictions of binary sorption isotherms for the sorption of heavy metals by pine bark using single isotherm data

The adsorption of three heavy metal ions by pine bark was studied. The study was divided into two parts; single component adsorption of the metals Cu2+, Cd2+ and Ni2+ and bisolute adsorption of the three binary systems Cu2+-Cd2+, Cu2+-Ni2+ and Cd2+-Ni2+. Extended Langmuir model, extended Freundlich model. Sips model and ideal adsorption solution theory (IAST) models were used to predict the equilibrium uptake for Cu2+, Cd2+ and Ni2+ in the binary diluted solutions using the single adsorption constants. The experimental data of single isotherm adsorption process were found to follow Langmuir isotherm model with less accuracy than Freundlich and Sips models. Whereas, the predictions of bisolute adsorption isotherms of the mentioned three systems, Cu2+-Cd2+, Cu2+-Ni2+ and Cd2+-Ni2+, showed good agreement with experimental data when using Extended-Langmuir, Extended-Freundlich and IAST. However, the only good fit of the Sips model was with the Cu2+-Cd2+ system.     

Effect of dye compounds on the adsorption of atrazine by natural sediment

The overall objective of this research is to investigate competitive adsorption between atrazine (AT) and dye compounds in the natural aquatic sediment. The sorbent was sediment obtained from Guanting Reservoir (Beijing, China), which contained 25% sand, 67% silt, 8% clay, and 2.06% organic carbon. Batch adsorption experiments were conducted at various Ca2+ concentration, pH levels, temperatures, and introducing conditions of dye compounds. Compared with the dye-free system, both of dyes including Congo red (CR) and methylene blue (MB) reduce the adsorption of atrazine over the range of dye concentrations examined, with the adsorption percentage of atrazine decreasing about 14-30%. And the competition between AT and MB is much stronger than that between AT and CR. The adsorption experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 1.669 micromol/kg for the MB-AT sample up to 3.738 micromol/kg for the AT-alone sample. By contrast with the single-solute adsorption isotherm, both simultaneous adsorption and dye preloading inhibit the adsorption of atrazine. As for AT preloading, the impacts of CR and MB are different on the desorption of atrazine. As compared to the atrazine desorption without dye compounds, a certain amounts of atrazine molecules are replaced by MB in AT preloading system, while in CR solution AT is adsorbed strongly on the sediment and could not be replaced by CR. The result suggests that micropore constriction by CR reduces the desorption rate of atrazine.     

Changes in water-extractability of soil inorganic phosphate induced by chloride and sulfate salts

GOAL, SCOPE AND BACKGROUND: One of the principal experimental variables which effect the results of phosphorus (P) sorption studies is the ionic composition, in addition to both species and concentrations of the contacting solution. In spite of the realization that ionic species, concentrations and their compositions effect P sorption and/or desorption, most of the salt-related studies are confined to Cl- (anion) in association with different cations. While the knowledge about the comparative response of P to Cl- and SO4(2-) ions was lacking, the current study was conducted to evaluate the comparative effects of anions (in association with cations) on inorganic P release and P fractions in the soil. METHODS: The test soil was amended with livestock compost manure (OP); KH2PO4 (IPk) or Ca(H2PO4)2 (IPc) at a rate of 1ppm. Soil was subjected to one salt and nine subsequent water extractions and different P fractions were measured. Four salt types, NaCl, Na2SO4, KCl and K2SO4, were used at levels of 0.5 M. RESULTS: Irrespective of P sources, P release was substantially increased in the salt-pretreated soil as compared to the non-saline soil. Sulfate salts released more P in subsequent water extractions than Cl-. Phosphorus release decreased for salt types with Na2SO4 > NaCl > K2SO4 > KCl and for P sources with OP approximately IPk > Control (without P application) > IPc, respectively. DISCUSSION: No previous study was found to compare the results of more P release by SO4(2-) than Cl- salt. Most of the previous studies focused on anion sorption capacities, but the mechanism for their adsorption is not fully known. Most of the authors suggested that the mechanisms of SO4(2-) and PO4(3-) adsorption are similar, and that both ions compete for the same sorption sites (Kamprath et al. 1956, Couto et al. 1979, Pasricha and Fox 1993). Although adsorbed SO4(2-) does not compete strongly with PO4(3-), there is likely to be some competition for sorption between these anions which may cause comparatively more P release by SO4(2-) than Cl- salts. Higher P release by Na-saturation could be due to the release of P associated with oxide surfaces or due to dissolution of Ca-P phases (Curtin et al. 1987). CONCLUSIONS: Study clearly showed that not only cations species differ for P desorption capacity, but associated anions also play a vital role in the fate of P under saline environments. Synergetic effects exist between Na and SO4(2-) ions which enhanced the P release. This study has also confirmed the fact that P from organic sources is available as well as from inorganic P sources. However, P release depends more on the type of P source applied than on total P. RECOMMENDATIONS AND PERSPECTIVES: It is highly recommended that more than one anion species must be used in the research plans for evaluating the P response in a saline environment. The results have important implications from the point of view of research, as most of the researchers focus on different cations only for evaluating P response to salts from an environmental point of view. However, our study has made it clear that anions in association with cations differed for their effects on P release.     

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.     

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.