Applied Catalysis B, Environmental (v.45, #2)
Catalytic decomposition of N2O over M x Co1−x Co2O4 (M = Ni, Mg) spinel oxides by Liang Yan; Tong Ren; Xiaolai Wang; Dong Ji; Jishuan Suo (85-90).
The catalytic decomposition of N2O to N2 and O2 was carried out on the M x Co1−x Co2O4 (M=Ni2+ and Mg2+, x=0.0–0.99) spinel catalysts. The results showed that the partial replacement of Co2+ by Ni2+ or Mg2+ in Co3O4 spinel oxide led to a significant improvement in the catalytic activity for the N2O decomposition, and the catalytic activity depended on the degree of Co2+ substitution by Ni2+ or Mg2+. The conversion of N2O reached 100% over the Ni0.74Co0.26Co2O4 and Mg0.54Co0.46Co2O4 catalysts at 200 °C and 300 °C in the absence and presence of excess O2 and water steam, respectively.
Keywords: Greenhouse gases; Nitrous oxide; N2O; Catalytic decomposition; Spinel oxide;
Catalytic activity of copper-zinc manganites for the reduction of NO and N2O by hydrocarbons by Giovanni Ferraris; Giuseppe Fierro; Mariano Lo Jacono; Marcello Inversi; Roberto Dragone (91-101).
The catalytic behaviour of copper-zinc manganites with general formula Cu x Zn1−x Mn2O4 (x=0, 0.01, 0.05, 0.10) was investigated for the reduction of NO by hydrocarbons. Also the N2O decomposition and its reduction by propane and propene were tested on representative samples. The catalysts were obtained by thermal decomposition at 973 K of carbonate precursors. Regardless the composition, all the precursors are monophasic and made by a rhodochrosite-like phase, Cu x Zn y Mn(1−x−y)CO3, in which Cu2+ and Zn2+ ions entered in solid solution. The metal dispersion in the precursors is preserved by the final catalysts that, in spite of the presence of copper, are monophasic and made by a Cu x Zn1−x Mn2O4 spinel-like phase. The reduction of NO was studied by using CH4, C3H8 and C3H6 as reducing agents and the last two hydrocarbons were used for testing the N2O reduction. Propene is the most effective hydrocarbon followed by propane whereas methane is efficient only at higher reaction temperatures. Pure zinc manganite is an active catalyst but the presence of copper in the spinel enhanced the catalytic activity of NO reduction by propane and slightly improved that of N2O reduction. Moreover, regardless the presence of copper, a high conversion (70–100%) of NO to N2 was attained at 873 K and the selectivity to N2 and CO2 was close to 1. The catalysts are stable in the CH4 and C3H8 containing streams within the whole range of temperature explored. By contrast, when C3H6 is used as reductant the spinel structure is preserved only below 773 K because at higher temperatures it collapses by reduction of Mn3+ to Mn2+ ions forming a mixture of ZnO and MnO oxides. At this stage the catalysts are still active and an attempt to explain this evidence is made.
Keywords: Copper-zinc manganites; NO reduction by methane; NO and N2O reduction by propane; NO and N2O reduction by propene;
SCR of NO by NH3 on alumina or titania-pillared montmorillonite various modified with Cu or Co by Lucjan Chmielarz; Piotr Kuśtrowski; Małgorzata Zbroja; Alicja Rafalska-Łasocha; Barbara Dudek; Roman Dziembaj (103-116).
Al2O3- and TiO2-pillared montmorillonites modified with Cu or Co were studied as catalysts of NO reduction with ammonia. Transition metals were introduced to pillared clays (PILCs) by ion exchange method or simultaneously with pillaring agent to the parent montmorillonite. The obtained materials were characterized using: XRF (composition), XRD (structure), BET and Horvath and Kawazoe (H–K) (texture) and NH3-TPD (acid centres). The clays intercalated with titania are significantly more active than alumina pillared ones. TiO2-intercalated montmorillonites modified with Cu have been found to be the most active catalysts in SCR of NO with ammonia in the low temperature region (250–450 °C), while Co-containing clays are much better at high temperatures (T>400 °C).
Keywords: Pillared montmorillonites; Titania; Alumina; Copper; Cobalt; Selective catalytic reduction; NO; Ammonia;
Pt catalysts supported on H-type zeolites for the catalytic combustion of chlorobenzene by Salvatore Scirè; Simona Minicò; Carmelo Crisafulli (117-125).
The deep oxidation of chlorobenzene was investigated over Pt catalysts supported on H-type zeolites (H-ZSM5 and H-beta). Pt/zeolite catalysts showed a higher activity compared to Pt/γ-Al2O3 samples which were tested for comparison. Within each class of zeolite, the activity of Pt/zeolite catalysts was found to be higher on the samples with lower SiO2/Al2O3 ratio. Amounts of polychlorinated benzenes (PhCl x ) were produced in the order Pt/H-ZSM5<Pt/H-beta<Pt/γ-Al2O3 and were found to be roughly independent of the SiO2/Al2O3 ratio of the zeolitic support. The trend in the PhCl x formation observed on Pt/zeolite samples, both in terms of total amount and relative distribution, was explained on the basis of a product shape selectivity effect induced by the zeolite, a lower size of zeolite channels hindering the further chlorination of PhCl to PhCl x .
Keywords: Catalytic combustion; Volatile organic compound (VOC); Chlorobenzene; Platinum; Zeolite; H-ZSM5;
Cloth catalysts in water denitrification by Yu. Matatov-Meytal; Yu. Shindler; M. Sheintuch (127-134).
Nitrite hydrogenation over Pd supported on an activated carbon cloth (ACC) has been investigated in an isothermal semi-batch reactor. The reaction is accompanied by increasing pH, which inhibits the reaction. The rate was corrected for pH changes and the reaction was found to be first-order with respect to nitrite concentration and zero-order with respect to hydrogen pressure. The corrected rate constant is of the form k eff =k exp[(pH−pzc)/(pH 0−pzc)], where k is the intrinsic constant and the pzc is the point of zero charge of catalyst surface. While Pd/ACC catalysts yield better rates than those of Pd supported on glass fiber cloth (GFC), they exhibit much poorer selectivity (in the unbuffered reaction conditions) due to ACC surface enrichment by hydrogen.
Keywords: Pd catalyst; ACC support; Liquid-phase hydrogenation; Nitrite; Nitrogen;
Effect of SO2 on CO and C3H6 oxidation over CeO2 and Ce0.75Zr0.25O2 by Subodh S Deshmukh; Minghui Zhang; Vladimir I Kovalchuk; Julie L d’Itri (135-145).
Ceria and Ce0.75Zr0.25O2 were characterized before and after SO2 exposure to determine the effect of sulfation on the structural, morphological and catalytic properties of the solids. The X-ray diffraction (XRD), scanning electron microscopy (SEM) data, and BET measurements show that both CeO2 and Ce0.75Zr0.25O2 are susceptible to crystallite grain size growth and surface area loss under exposure to gaseous mixtures containing 20–40 ppm SO2 at 600 °C. The Ce0.75Zr0.25O2 is more resistant to morphological changes than CeO2. However, no bulk sulfites/sulfates were detected with either oxide. Both presulfation of the oxides and addition of 20 ppm SO2 to a 1% CO+2% O2+N2 reaction mixture results in a significant suppression of the CO oxidation reaction. The effect of SO2 on CO oxidation was much less pronounced for the Ce0.75Zr0.25O2 than for the CeO2. Surprisingly, 20 ppm SO2 in the 1100 ppm C3H6+2% O2+N2 reaction mixture has a promoting effect on the oxidation of C3H6 catalyzed by CeO2. The influence of SO2 in the feed gas on the CO and C3H6 oxidation is discussed in terms of different mechanisms for these reactions.
Keywords: Ceria; Ceria–zirconia; Sulfur dioxide; CO oxidation; Propylene oxidation; SO2-induced sintering;
Catalytic decomposition/regeneration of Pt/Ba(NO3)2 catalysts: NO x storage and reduction by David James; Elodie Fourré; Masaru Ishii; Michael Bowker (147-159).
The introduction of lean-burn engine technology has prompted the development of NO x storage-reduction (NSR) catalysts, which are currently based on a Pt/Ba(NO3)2/Al2O3 system. In this work a series of powdered catalysts based on this system were prepared and their reactivities examined with a pulsed-flow reactor, which was used to carry out temperature programmed desorption (TPD) experiments and to simulate the NSR reaction itself. TPD experiments reveal that Ba(NO3)2 is catalytically decomposed by the presence of Pt, at a significantly lower temperature than otherwise (by >200 K), with the extent of the decomposition being dependent on the amount of Pt loaded. The products formed from the decomposition depend on the oxidation state of the Pt; firstly N2 and N2O are evolved (formed from cracking of the NO produced via the Ba(NO3)2 decomposition), but as the adsorbed oxygen resulting from their formation builds up, NO and O2 appear and N2 and N2O are lowered. NO x storage has been shown to occur even at room temperature following Ba(NO3)2 decomposition from a 0.5 wt.% Pt/Al2O3 catalyst impregnated with 10 wt.% Ba(NO3)2. These experiments can be carried out in a reversible way. Simulations of the NSR reaction, using H2 and CO as reductants, indicate a remarkable difference between the two; CO appears to facilitate Ba(NO3)2 decomposition, but not NO x reduction, whereas H2 enables both to take place, with excellent conversion to N2. The difference between the two reductants in these experiments reflects the difference in binding between the two adsorbates and consequent Pt surface poisoning by CO.
Keywords: NO x storage; NO x reduction; Barium nitrate decomposition; Platinum; Influence of reductant;
Sol–gel synthesis of vanadia–silica for photocatalytic degradation of cyanide by Adel Ali Ismail; Ibrahim Ahmed Ibrahim; Reda Mohamedy Mohamed (161-166).
Cyanides used in some chemical synthesis and metallurgical processes are highly toxic and must be destroyed or removed from wastewaters prior to discharge. Vanadia–silica xerogel as photocatalyst has been prepared via sol–gel technique by dissolving ammonium metavanadate (AMV) and tetraethylorthosilicate (TEOS) and applied for photodegradation of cyanide from solution. The optimum conditions for preparation of V2O5–SiO2 gel is 1:1 of vanadium/silicon (V/Si) molar ratio and TEOS:H2O:C2H5OH is 1:8:4 mole ratios at 30 °C for 10 min, at these conditions the photoactivity of V2O5–SiO2 was 98.5% at surface area 310 m2/g. The calculated activation energy of the reaction between AMV and TEOS was found to be −10.81 kcal/g. The optimum loading of vanadia–silica xerogel was 0.166 wt.% that give 98.5% cyanide removal efficiency after 3 h. The overall kinetics of photodegradation of cyanide using vanadia–silica photocatalyst was found to be of first order.
Keywords: Sol–gel; V2O5–SiO2; Xerogel; Photocatalytic; Cyanide;