Synergetic catalytic removal of Hg0 and NO over CeO2(ZrO2)/TiO2

A series of CeO₂(ZrO₂)/TiO₂ monolith catalysts were investigated for catalytic oxidation of Hg⁰ and NH₃-SCR of NO. Effect of flue gases components on catalytic oxidation of Hg⁰ was mainly studied. Results showed that the CeO₂(ZrO₂)/TiO₂ catalyst exhibited high efficiency for catalytic oxidation of Hg⁰ at 240–400 °C without adding other oxidant, and its catalytic performance for NH₃-SCR of NO was not affected. NH₃ had slight inhibitory effect while SO₂ and NO had no influence on catalytic oxidation of Hg⁰, but O₂ obviously improved catalytic oxidation of Hg⁰ for its oxidation susceptibility.     

Experimental and theoretical analysis of element mercury adsorption on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag composites

A novel magnetic nano-sorbent Fe₃O₄/Ag was synthesized and applied to capture the elemental mercury from the simulated flue gas. The morphology, components and crystal phase of the sorbents were characterized by transmission electron microscope (TEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD), respectively. The mercury removal performance of the sorbents was investigated through the fixed-bed tests. The results indicated that silver was successfully loaded on the surface of Fe₃O₄ particles, which could significantly enhance the Hg⁰ removal performance of the sorbents. Flue gas components, including CO₂, SO₂, and NO, have little impact on the Hg⁰ removal performance of Fe₃O₄/Ag sorbents, while O₂ has a slightly positive effect. The Hg⁰ removal efficiency decreased with the increasing of temperature, Hg⁰ inlet concentration and gas hourly space velocity. Only one broad mercury desorption peak at approximately 210 °C could be observed during the temperature-programmed desorption (TPD) process, which indicated that mercury species existing on the surface of Fe₃O₄/Ag sorbents might be elemental mercury instead of oxidized mercury. Furthermore, the reusability tests showed that the Fe₃O₄/Ag sorbents could be efficiently regenerated and reused. Finally, the theoretical analysis based on the DFT method showed that a weak chemisorption of Hg⁰ on Fe₃O₄ sorbents changed to a strong chemisorption when silver was loaded. The results of theoretical analysis conformed to the experiments results well.     

The Effect of CH<Subscript>4</Subscript> on NH<Subscript>3</Subscript>-SCR Over Metal-Promoted Zeolite Catalysts for Lean-Burn Natural Gas Vehicles

We present a systematic investigation of the deNO_x activity of two commercial metal exchanged zeolite NH₃-SCR catalysts, a Cu-SAPO and a Fe-BEA, in view of their application to the exhaust after-treatment systems of lean-burn natural gas vehicles. The catalytic activity data collected under realistic operating conditions, representative of the after-treatment system of lean-burn vehicles, were compared to those obtained adding methane to the gas feed stream in order to assess the impact of this hydrocarbon, which is usually emitted from natural gas engines, on the NH₃-SCR catalytic chemistry. Our results indicate a negligible impact of methane on the SCR activity at all conditions, but in the presence of a large excess of NO₂ at T?>?400 °C due to methane oxidation by NO₂. The data collected over the two individual metal-promoted zeolites were also compared with those obtained combining both catalysts in sequential arrangements, in order to take advantage of their complementary high activities in different temperature ranges. The Fe-zeolite?+?Cu-zeolite sequence outperformed the two individual components in terms of both overall deNOx efficiency and N₂O selectivity, and was equally insensitive to methane.     

Preliminary evaluation of NaClO<Subscript>2</Subscript> powder injection method for mercury oxidation: Bench scale experiment using iron-ore sintering flue gas

The injection of powdered sodium chlorite (NaClO₂(s)) for mercury oxidation into iron-ore sintering flue gas has been evaluated by using the bench scale of tubular flow reactor, where the flow rate and temperature of flue gas stream were controlled to 250 Nm³ hr⁻¹ and 135 °C, respectively, and either 50 or 260 μg Nm⁻³ of the mercury concentration was introduced intentionally to the gas stream. We have observed that 90% of Hg⁰ oxidation was obtained at 0.18 g Nm⁻³ NaClO₂(s) injection, indicating that the oxidized weight of Hg° by the loaded weight of NaClO₂(s) is 1026 (±333) (μg-Hg⁰) (g-NaClO₂(s))⁻¹. This result leads us to suggest that the simple injection of NaClO₂(s) into the flue gas has the potential to achieve over 90% mercury control in practical application.     

Effects of copper loading on NH<Subscript>3</Subscript>-SCR and NO oxidation over Cu impregnated CHA zeolite

Cu/CHA catalysts with various Cu loadings (0.5 wt%–6.0 wt%) were synthesized via incipient wetness impregnation. The catalysts were applied to the selective catalytic reduction (SCR) of NO with NH₃ and NO oxidation reaction. XRD and N₂ adsorption-desorption data showed that CHA structure was maintained with the incorporation of Cu, while specific surface areas decreased with increasing Cu loading. At intermediate Cu loading, 4 wt%, the highest NH₃-SCR activity was observed with ～98% N₂ selectivity from 150 °C to 300 °C. Small amounts of water, 2%, slightly increased NO conversion in addition to the remarkable N₂O and NO₂ reduction at high temperature. Water effects are attributed to the improved Cu ion reducibility and mobility. NO oxidation results provided no relation between NO₂ formation and SCR activity. Physicochemical properties, NO conversion, N₂ selectivity, and activation energy data showed that impregnated samples’ molecular structure and catalytic activity are comparable to the conventional ion-exchanged (IE) samples’ ones.     

Effect of Nickel as Dopant in Mn/TiO<Subscript>2</Subscript> Catalysts for the Low-Temperature Selective Reduction of NO with NH<Subscript>3</Subscript>

Nickel doped manganese oxide supported on titania materials were investigated for the low-temperature NH₃-SCR. For this purpose, a series of Ni modified Mn/TiO₂ catalysts were prepared and evaluated for the low-temperature SCR of NO with ammonia in the presence of excess oxygen. The catalytic performance of these materials was compared with respect to the nickel weight percentage in order to examine the correlation between physicochemical characteristics and reactivity of optimized materials. It was found that the 5% Mn–2% Ni/TiO₂ catalyst showed the highest activity and yielded 100% NO conversion at 200 °C. XRD results reveal highly dispersed manganese–nickel species on TiO₂ support for the Mn–Ni/TiO₂ catalysts. Our TPR data results suggested an increase in reducibility of manganese species in Mn–Ni/TiO₂ catalysts. The absence of the high-temperature (736 K) peak indicates that the dominant phase is MnO₂. This increase of reducibility and dominant MnO₂ phase seems to be the reason for the enhanced activity and time on stream patterns of nickel-promoted titania-supported manganese catalysts. BET results illustrate that the high NO conversion is strongly dependant on the specific surface area and pore volume of this catalyst. All the physicochemical techniques we used suggested that the composition of manganese and nickel oxides on the support surface is playing an important role for the enhancement of NO conversion and the prominent time on stream stability.     

Enhancement of NO absorption in ammonium-based solution using heterogeneous Fenton reaction at low H<Subscript>2</Subscript>O<Subscript>2</Subscript> consumption

A novel NO removal system is designed, where NO is initially oxidized by ?OH radicals from the decomposition of hydrogen peroxide (H₂O₂) over hematite and then absorbed by ammonium-based solution. According to the high performance liquid chromatography (HPLC) profile and the isopropanol injection experiments, the ?OH radicals are proved to play a critical role in NO removal. The NO removal efficiency primarily depends on H₂O₂ concentration, gas hourly space velocity (GHSV), H₂O₂ feeding rate and reaction temperature, while the flue gas temperature slightly affects the NO removal efficiency. The low H₂O₂ consumption makes this system a promising technique in NO removal process using wet-method. The evolution of catalyst in reaction is analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The nitrite ion and nitrate ion in aqueous solution are detected by the continuous phase flow analyzer. Finally, the macrokinetic parameters of the NO oxidation are obtained by using the initial rate method.     

Investigating active centers of industrial catalysts for the oxidative chlorination of ethylene on a γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> surface

Selecting the best catalyst for large-scale industrial processes of the oxychlorination of ethylene (OCE) is a practical task of great importance. In such processes, even a slight reduction in selectivity results in considerable losses of raw materials. The enhancement of selectivity requires knowledge of the structure of the catalysts’ surfaces and the mechanism of the process of oxidative chlorination of ethylene into 1,2-dichloroethane (1,2-DCE). The structure of active sites of copper chloride catalysts on the surface of alumina was studied by physicochemical methods of IR spectroscopy and DTA. The structure was described for the active sites of catalysts for the oxidative chlorination of ethylene into (1,2-DCE) of two types, CuCl₂ and CuCl on γ-Al₂O₃: H1 (Harshow, United States) and OXYMAX-B (MEDC-B) (Sǜd-Chemie Catalysts, Germany). It was ascertained that complex compounds with [CuCl₄]⁻² and [CuCl₂]⁻¹ are formed upon interaction between the active phase of the catalyst (copper chlorides CuCl₂ or CuCl), and the surface groups of the support γ-Al₂O₃ (≡Al-OH) (this observation does not fall into the known theory of their structure). In accordance with the results from our study, a method was elaborated for synthesizing a catalyst with the optimum properties for OCE, and a pilot setup for the detailed investigation of this process was built. The possibility of cutting ethylene losses in half during deep oxidation and eliminating the formation of side products by a factor of 1.5–2 was demonstrated by the industrial production of 1,2-DCE and vinyl chloride at OOO Karpatnaftokhim in Kalush. The method for producing 1,2-DCE is protected by a Ukranian patent.     

Effect of H<Subscript>2</Subscript>O<Subscript>2</Subscript> modification of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>@carbon for m-xylene oxidation to isophthalic acid

The production of isophthalic acid (IPA) from the oxidation of m-xylene (MX) by air is catalyzed by H₃PW₁₂O₄₀ (HPW) loaded on carbon and cobalt. We used H₂O₂ solution to oxidize the carbon to improve the catalytic activity of HPW@C catalyst. Experiments reveal that the best carbon sample is obtained by calcining the carbon at 700 °C for 4 h after being impregnated in the 3.75% H₂O₂ solution at 40 °C for 7 h. The surface characterization displays that the H₂O₂ modification leads to an increase in the acidic groups and a reduction in the basic groups on the carbon surface. The catalytic capability of the HPW@C catalyst depends on its surface chemical characteristics and physical property. The acidic groups play a more important part than the physical property. The MX conversion after 180 min reaction acquired by the HPW@C catalysts prepared from the activated carbon modified in the best condition is 3.81% over that obtained by the HPW@C catalysts prepared from the original carbon. The IPA produced by the former is 46.2% over that produced by the latter.     

Reduction of CO<Subscript>2</Subscript> to CO via reverse water-gas shift reaction over CeO<Subscript>2</Subscript> catalyst

CeO₂ catalysts with different structure were prepared by hard-template (Ce-HT), complex (Ce-CA), and precipitation methods (Ce-PC), and their performance in CO₂ reverse water gas shift (RWGS) reaction was investigated. The catalysts were characterized using XRD, TEM, BET, H₂-TPR, and in-situ XPS. The results indicated that the structure of CeO₂ catalysts was significantly affected by the preparation method. The porous structure and large specific surface area enhanced the catalytic activity of the studied CeO₂ catalysts. Oxygen vacancies as active sites were formed in the CeO₂ catalysts by H₂ reduction at 400 °C. The Ce-HT, Ce-CA, and Ce-PC catalysts have a 100% CO selectivity and CO₂ conversion at 580 °C was 15.9%, 9.3%, and 12.7%, respectively. The highest CO₂ RWGS reaction catalytic activity for the Ce-HT catalyst was related to the porous structure, large specific surface area (144.9 m²?g^?1) and formed abundant oxygen vacancies.     

Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde over SiO2 Supported Nickel Phosphide Catalysts

The heterogeneous mercury reaction mechanism, reactions among elemental mercury (Hg⁰) and simulated flue gas across laboratory-scale selective catalytic reduction (SCR) reactor system was studied. The surface of SCR catalysts used in this study was analyzed to verify the proposed reaction pathways using transmission electron microscopy with energy dispersive X-ray analyses (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The Langmuir–Hinshelwood mechanism was proven to be most suitable explaining first-layer reaction of Hg⁰ and HCl on the SCR catalyst. Once the first layer is formed, successive layers of oxidized mercury (HgCl₂) are formed, making a multi-layer structure.     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Quantification and redox property of the oxygen-bridged Cu<Superscript>2+</Superscript> dimers as the active sites for the NO decomposition over Cu-ZSM-5 catalysts

For a range of Cu-ZSM-5 catalysts with different Cu-exchange levels on the two kinds of ZSM-5 with different Si/A1 ratios, temperature programmed reduction using CO (CO-TPR) followed by H₂ (H₂-TPR), and temperature programmed desorption of oxygen (O₂-TPD) were conducted using an online mass spectrometer to characterize and quantify the copper species on the catalysts in the calcined state. Copper species on the ZSM-5 were quantitatively characterized as Cu²⁺, (Cu-O-Cu)²⁺ and CuO after calcination in oxygen environment. The N₂ formation activities of the catalysts in the decomposition of NO were well correlated with the quantified catalytic amounts of the Cu²⁺ ions involved in the Cu-dimers, (Cu-O-Cu)²⁺. The mol fraction of the Cu ions present as the Cu-dimers increased at the sacrifice of the isolated Cu²⁺ with increasing Cu ion exchange level, suggesting that the species could be formed between the two Cu²⁺ in close proximity. Oxygen that could be thermally desorbed from the oxidized catalysts in the O₂-TPD was responsible for the reduction of the Cu-dimers. It was concluded that the decomposition of NO over Cu-ZSM-5 catalyst proceeded by the redox of (Cu-O-Cu)²⁺, as active centers. With the temperature programmed surface reaction using N₂O or NO over an oxidized catalyst sample as well as the O₂-TPD, it was possible to estimate the change of the oxidation state of the Cu ions engaged in the Cu-dimers.     

Pd/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts on cellular supports for VOC vapor neutralization

The results from investigating the influence of temperature, concentration, and flow rate on the catalytic oxidation of vapors of volatile organic compounds (VOCs) in the presence of Pd/γ-Al₂O₃ catalyst on cellular supports are presented. The activity of Pd/γ-Al₂O₃ catalysts on ceramic and metal monolith supports with a cellular structure during the catalytic neutralization of VOC (ethanol, ethyl acetate) vapors under laboratory conditions was determined, and the most stable catalyst for the preliminary study of a large batch was chosen. A pilot unit was created to test a large batch of cellular monolith catalyst in neutralizing VOC vapors under conditions of flexographic production. It was established that a high rate of conversion (> 99 %) was achieved for VOC concentrations of 0.5 g/m³ at space velocities of up to ∼10⁴ h⁻¹, and for VOC concentrations of 5.0 g/m³ at space velocities of up to ∼5 × 10⁵ h⁻¹. The change in the activity of the catalysts on metal (nickel alloyed by aluminum) and ceramic cellular supports in service was investigated. After 300–500 min of operation, virtually complete deactivation of catalyst on a metal support was observed, accompanied by the formation of nickel oxide and acetate. Pilot unit tests with catalyst on cellular supports having a volume of 14.5 l in neutralizing the ventilation exhausts of flexographic production confirmed the possibility of more than 90% conversion at VOC concentrations of ∼0.1 g/m³ and more than 97% at VOC concentrations of over 1 g/m³. A consistently high conversion of VOC was observed during a 100 h test of the pilot unit. A system for recovering the heat released during VOC oxidation lowers the operating costs of the pilot unit.     

Effects of NOx, α-Fe2O3, γ-Fe2O3, and HCl on mercury transformations in a 7-kW coal combustion system

Bench-scale investigations indicate that NO, NO₂, hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃), and HCl promote the conversion of gaseous elemental mercury (Hg⁰) to gaseous oxidized mercury (Hg²⁺) and/or particle-associated mercury (Hg[p]) in simulated coal combustion flue gases. In this investigation, the effects of NO_x, α-Fe₂O₃, γ-Fe₂O₃, and HCl on Hg transformations were evaluated by injecting them into actual coal combustion flue gases produced from burning subbituminous Absaloka and lignitic Falkirk coals in a 7-kW down-fired cylindrical furnace. A bituminous Blacksville coal known to produce an Hg²⁺-rich combustion flue gas was also burned in the system. The American Society for Testing and Materials Method D6784-02 (Ontario Hydro method) or an online Hg analyzer equipped to measure Hg⁰ and total gaseous mercury (Hg[tot]) was used to monitor Hg speciation at the baghouse inlet (160–195 °C) and outlet (110–140 °C) locations of the system. As expected, the baseline Blacksville flue gas was composed predominantly of Hg²⁺ (Hg²⁺/Hg[tot]=0.77), whereas Absaloka and Falkirk flue gases contained primarily Hg⁰ (Hg⁰/Hg[tot]=0.84 and 0.78, respectively). Injections of NO₂ (80–190 ppmv) at 440–880 °C and α-Fe₂O₃ (15 and 6 wt.%) at 450 °C into Absaloka and Falkirk coal combustion flue gases did not significantly affect Hg speciation. The lack of Hg⁰ to Hg²⁺ conversion suggests that components of Absaloka and Falkirk combustion flue gases and/or fly ashes inhibit heterogeneous Hg⁰–NO_x–α-Fe₂O₃ reactions or that the flue gas quench rate in the 7-kW system is much different in relation to bench-scale flue gas simulators.An abundance of Hg²⁺, HCl, and γ-Fe₂O₃ in Blacksville flue gas and the inertness of injected α-Fe₂O₃ with respect to heterogeneous Hg⁰ oxidation in Absaloka and Falkirk flue gases suggested that γ-Fe₂O₃ catalyzes Hg²⁺ formation and that HCl is an important Hg⁰ reactant. The filtration of Absaloka and Falkirk combustion flue gases at 150 °C through fabric filters with ≈60 g/m² γ-Fe₂O₃ indicated that about 30% of the Hg⁰ in Absaloka and Falkirk flue gases was converted to Hg²⁺ and/or Hg(p). HCl injection (100 ppmv) into the Absaloka combustion flue gas converted most of the Hg⁰ to Hg²⁺, whereas HCl injection into the Falkirk flue gas converted most of the Hg⁰ and Hg²⁺ to Hg(p). Additions of γ-Fe₂O₃ and HCl did not have a synergistic effect on Hg⁰ oxidation. The filtration of Absaloka and Falkirk flue gases through much greater fabric filter loadings of 475 g/m² γ-Fe₂O₃ essentially doubled the baghouse Hg[tot] removal efficiency to about 50%. Results from this investigation demonstrate the importance of evaluating potential Hg⁰ reactants and oxidation catalysts in actual coal combustion flue gases.     

Partial oxidation of methane over Ni/Ce-Zro<Subscript>2</Subscript>/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The catalytic behavior of Ni/Ce-ZrO₂/θ-Al₂O₃ has been investigated in the partial oxidation of methane (POM) toward synthesis gas. The catalyst showed high activity and selectivity due to the heat treatment of the support and the promotional effect of Ce-ZrO₂. It is suggested that the support was stabilized through the heat treatment of γ-Al₂O₃ and the precoating of Ce-ZrO₂, on which a protective layer was formed. Moreover, sintering of the catalyst was greatly suppressed for 24 h test. Pulse experiments of CH₄, O₂ and/or CH₄/O₂ with a molar ratio of 2 were systematically performed over fresh, partially reduced and well reduced catalyst. Results indicate that CH₄ can be partially oxidized to CO and H₂ by the reactive oxygen in complex NiO_x species existing over the fresh catalyst. It is demonstrated that POM over Ni/Ce-ZrO₂/θ-Al₂O₃ follows the pyrolysis mechanism, and both the carbonaceous materials from CH₄ decomposition over metallic nickel and the reactive oxygen species present on NiO_x and Ce-ZrO₂ are intermediates for POM.     

Selective oxidation of H<Subscript>2</Subscript>S to sulfur over CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> catalyst

The catalytic oxidation of hydrogen sulfide (H₂S) to elemental sulfur was studied over CeO₂-TiO₂ catalysts. The synthesized catalysts were characterized by various techniques such as X-ray diffraction, BET, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia, and scanning electron microscopy (SEM). Catalytic performance studies of the CeO₂-TiO₂ catalysts showed that H₂S was successfully converted to elemental sulfur without considerable emission of sulfur dioxide. CeO₂-TiO₂ catalysts with Ce/Ti=1/5 and 1/3 exhibited the highest H₂S conversion, possibly due to the uniform dispersion of metal oxides, high surface area, and high amount of acid sites.     

An on-line infrared spectroscopic system with a modified multipath White cell for direct measurements of N<Subscript>2</Subscript>O from NH<Subscript>3</Subscript>-SCR reaction

An on-line, continuous IR-based N₂O measurement system has been developed by combining with a variable multipath “White cell” to avoid a huge amount of the well-known artifact errors in actual N₂O concentrations determination when analyzing grab samples taken from stationary sources, such as fossil fuel-fired power plants. For solving the problems confronted in earlier stages of this study, the gas cell had to have modifications of the feed through of gas sample flows, the multilayer coatings of stainless steel mirrors, and the thermal efficiency to provide high cell inner temperatures in flowing gas samples. These modifications allow good tolerance of the gas cell to gases and chemicals, such as NO _x and NH₃, and NH₄NO₃ driven from them, and its usage for a long lifetime even under harsh conditions. They also offer excellent performance not only in directly determining the extent of N₂O formation during the course of NH₃-SCR reaction over a sample of a commercial V₂O₅-WO₃/TiO₂ catalyst, but also in simultaneously monitoring changes in concentrations of NO, NO₂ and NH₃ during the reaction. Each reference peak was chosen in gasphase spectra for N₂O, NO _x , NH₃ and H₂O, and CO₂ as a possible interference, and the modified gas cell was finely tuned to obtain their spectra with a high resolution under optimal operating conditions. The catalyst gave significant amounts of N₂O formation at reaction temperatures greater than 350 °C, and attention should be paid to the possibility of N₂O production from commercial NH₃-SCR deNO _x processes with V₂O₅/TiO₂-based catalysts.     

V-promoted Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for synthetic natural gas (SNG) production: Catalyst preparation methodologies

The effect of preparation method on the catalytic performance of V-promoted Ni/Al₂O₃ catalysts for synthetic natural gas (SNG) production via CO methanation has been investigated. The Ni-V/Al₂O₃ catalysts were prepared by co-impregnation (CI) method, deposition precipitation (DP) method as well as two sequential impregnation (SI) methods with different impregnation sequence. Among the prepared catalysts, the one prepared by CI method exhibited the best catalytic performance due to its largest H₂ uptake and highest metallic Ni dispersion. In a 91h-lifetime test, this catalyst showed high stability at high temperature and weight hourly space velocity. This work demonstrates that the catalytic performance of the V-promoted Ni/Al₂O₃ catalysts can be improved by carefully controlling the preparation method/conditions.     

Electrochemical modification of the catalytic activity of TiO<Subscript>2</Subscript>/YSZ supported rhodium films

The electrochemical activation of ethylene oxidation was studied over rhodium catalysts of different thickness (40, 100 and 160 nm) sputtered on top of a thin layer of TiO₂ deposited on YSZ. The strong relationship between catalytic activity and oxidation state of rhodium was confirmed. Under open-circuit operation the catalyst potential appears as a suitable indicator of the surface oxidation state of rhodium allowing a prediction of the catalytic behavior from solid electrolyte potentiometric measurements. Under closed-circuit conditions the catalyst potential was used as a tool to tune the catalytic activity of rhodium which showed increasing promotional efficiency with decreasing catalyst film thickness.