Catalytic reduction of N2O by H2 over well-characterized Pt surfaces

A 0.65% Pt/SiO₂ catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N₂O reduction by H₂ at very low temperatures, such as 363 K. The supported Pt with a high dispersion of 92% gave no presence of O atoms remaining on an H-covered Pt _s , based on in situ DRIFTS spectra of CO adsorbed on Pt _s after either N₂O decomposition at 363 K or subsequent exposure to H₂ for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H₂O produced by introducing H₂ at 363 K onto the oxidized Pt _s . Dissociative N₂O adsorption at 363 K on Pt _s was not inhibited by the H₂O_(ad) on the silica surface but not on Pt _s , as acquired by IR peaks at 3,437 and 1,641 cm⁻¹, in very consistent with the same hydrogen coverage, established via H₂-N₂O titration on a reduced Pt _s , as that revealed upon the titration reaction with a fully wet surface on which all bands and their position in IR spectra for CO are very similar to that obtained after H2 titration on a reduced Pt _s . Based on the characterization using chemisorption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N₂O decomposition at 363 K after a certain on-stream hour, depending significantly on N₂O concentrations used, is due to self-poisoning by the strong chemisorption of O atoms on Pt _s , while the presence of H₂ as a reductant could readily catalyze continuous N₂O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Preferential CO Oxidation on Bimetallic Pt<Subscript>0.5</Subscript>M<Subscript>0.5</Subscript> Catalysts (M = Fe,Co, Ni) Prepared from Double Complex Salts

Properties of Pt_0.5M_0.5 nanopowders (M = Fe, Co, Ni) of alloys obtained via the decomposition of double complex salts [Pt(NH₃)₅Cl][Fe(C₂O₄)₃] ? 4H₂O, [Pt(NH₃)₄][Co(C₂O₄)₂(H₂O)₂] ? 2H₂O, and [Pt(NH₃)₄][Ni(C₂O₄)₂(H₂O)₂] ? 2H₂O, respectively, are studied in the reaction of preferential CO oxidation. It is shown that bimetallic Pt_0.5M_0.5 catalysts (M = Fe, Co, Ni) are much more active in the low temperature range than Pt nanopowder. The activity of the catalysts decreases in the order Pt_0.5M_0.5 ≥ Pt_0.5M_0.5 > Pt_0.5M_0.5 @ Pt. The higher activity of bimetallic Pt0.5M0.5 catalysts in the reaction of preferential CO oxidation in the low-temperature range under conditions of dense Pt surface coverage by adsorbed CO molecules is most likely caused by the activation of CO on Pt atoms, the activation of O₂ on atoms of the second metal (Fe, Co, Ni), and the reaction that occurs at the sites of contact between the atoms of platinum and the atoms of the second metal on the surfaces of the alloy’s nanoparticles. The bimetallic systems investigated in this work can be used to improve catalysts of practically important preferential CO oxidation reaction. These systems have considerable potential in the afterburning reactions of CO and hydrocarbons; hydrogenation reactions; electrochemical reactions; and many others. The means used in the preparation of bimetallic nanopowders based on the decomposition of double complex salts is simple, does not require the use of expensive or complex reagents, and can be easily adapted to produce supported catalysts containing Pt_0.5M_0.5 metal alloys (M = Fe, Co, Ni).     

Emissions of N<Subscript>2</Subscript>O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N₂O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N₂O ha⁻¹ year⁻¹ for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N₂O ha⁻¹ year⁻¹. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N₂O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N₂O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N₂O emissions such as groundwater level. In this paper we report on the relations between N₂O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N₂O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N₂O–N ha⁻¹ year⁻¹ and 11.6 kg N–N₂O ha⁻¹ year⁻¹ for the dry and wet conditions, respectively. Especially under dry conditions, measured N₂O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N₂O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R ² = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.     

The physical solubilities and diffusivities of N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> in aqueous ammonia solutions on the additions of AMP,glycerol and ethylene glycol

Carbon dioxide (CO₂) is a major greenhouse gas, the emissions of which should be reduced. There are various technologies for the effective separation of CO₂. Of these, chemical absorption methods are generally accepted as the most effective. The monoethanolamine (MEA) process is an effective way to remove CO₂, but is an expensive option for the separation of CO₂ from massive gas-discharging plants. Therefore, ammonia solution, which is less expensive and more effective than MEA, was used for the removal of CO₂. In this study, the physical solubility of N₂O in (ammonia+water), (ammonia+2-amino-2-methyl-1-propanol+water), (ammonia+glycerol+water) and (ammonia+ ethylene glycol+water) was measured at 293, 303, 313, 323 K. Additive concentrations of 1, 3, and 5 wt% AMP, glycerol and ethylene glycol were added for each 9 wt% ammonia solution. A solubility apparatus was used to investigate the solubility of N₂O in ammonia solutions. The diffusivity was measured with a wetted wall column absorber. The “N₂O analogy” is used to estimate the solubility and diffusivity of CO₂ in the aqueous ammonia solutions. OriginPro 7.5 was used to correlate the solubility and diffusivity of N₂O in ammonia solutions. The parameters of the correlation were determined from the measured solubility and diffusivity.     

Reaction kinetics of phenol synthesis through one-step oxidation of benzene with N<Subscript>2</Subscript>O over Fe-ZSM-5 zeolite

Based on the information from GC-MS on-line measurement and thermodynamic analysis, the reaction network of gas-phase hydroxylation of benzene with nitrous oxide over Fe-ZSM-5 zeolite was systematically investigated. The main reactions and side reactions were identified, and a kinetic reaction network was proposed as follows: benzene+N₂O→phenol→CO/CO₂. According to the mechanism, the experimental results were interpreted reasonably. The hydroxylation kinetic experiments were carried out in an isothermal integral microreactor under the conditions of n(benzene)/n(N₂O)=8–12, T=663–763 K and atmospheric pressure. Based on the reaction network proposed, the parameters in the rate model of power-law were estimated by means of Gauss-Newton optimal method with the Levenberg-Marquardt modifications, and the results were in good agreement with the experimental data.     

N<Subscript>2</Subscript>O fluxes and CO<Subscript>2</Subscript> exchange at different N doses under elevated CO<Subscript>2</Subscript> concentration in boreal agricultural mineral soil under <Emphasis Type="Italic">Phleum pratense</Emphasis>

The effects of elevated atmospheric CO₂ concentration on N₂O fluxes, instant CO₂ exchange and the biomass production of timothy (Phleum pratense) were studied in the laboratory. Three sets of 12 farmed sandy soil mesocosms sown with Phleum pratense were fertilised with a commercial fertiliser in order to add 5, 10 and 15 g N m⁻², and equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹), and in the other two at double the ambient concentration (720 μmol mol⁻¹). Forage was harvested and the plants fertilised twice during the N₂O measurements. This was followed by an extra fertilisation and harvesting. After the third harvest, the growth of P. pratense was maintained at a height of 18 cm for measurements of instant CO₂ exchange, performed in two growth chambers. N₂O exchange was monitored using a closed chamber technique and a gas chromatograph. Instant CO₂ exchange was monitored using an infrared gas analyser. N₂O was emitted from the soil in the low, moderate and high N treatments at both CO₂ concentrations when the moisture content was low, the N₂O probably being mainly derived from nitrification. The highest flux (3303 μg N₂O m⁻² h⁻¹) occurred in the highest N treatment before thinning the stand of P. pratense under elevated CO₂ concentration. P. pratense was acclimated to the elevated CO₂ concentration: the NEE and P _G of the elevated growth of P. pratense decreased, in contrast to the fluxes of the normal ambient growth, when measured at the changed CO₂ concentration (ambient). The rate of respiration (R _TOT) in the agroecosystem did not increase due to the elevated CO₂ concentration, but instead the results indicated decreased R _TOT (on average 2049 and 1808 mg CO₂ m⁻² h⁻¹ at ambient and elevated CO₂ concentration, respectively) when there was an abundant N supply. This infers the possibility of enhanced C accumulation in agriculture mineral soil via P. pratense under an increased atmospheric CO₂ supply.     

Structure and electrical properties of sputtered TiO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> bilayer composite dielectrics upon annealing in nitrogen

The high-k dielectric TiO₂/ZrO₂ bilayer composite film was prepared on a Si substrate by radio frequency magnetron sputtering and post annealing in N₂ at various temperatures in the range of 573 K to 973 K. Transmission electron microscopy observation revealed that the bilayer film fully mixed together and had good interfacial property at 773 K. Metal-oxide-semiconductor capacitors with high-k gate dielectric TiO₂/ZrO₂/p-Si were fabricated using Pt as the top gate electrode and as the bottom side electrode. The largest property permittivity of 46.1 and a very low leakage current density of 3.35 × 10^-5 A/cm² were achieved for the sample of TiO₂/ZrO₂/Si after annealing at 773 K.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

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.     

Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Dye sensitized CO<Subscript>2</Subscript> reduction over pure and platinized TiO<Subscript>2</Subscript>

TiO₂ thin and thick films promoted with platinum and organic sensitizers including novel perylene diimide dyes (PDI) were prepared and tested for carbon dioxide reduction with water under visible light. TiO₂ films were prepared by a dip coating sol–gel technique. Pt was incorporated on TiO₂ surface by wet impregnation [Pt(on).TiO₂], or in the TiO₂ film [Pt(in).TiO₂] by adding the precursor in the sol. When tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate was used as sensitizer, in addition to visible light activity towards methane production, H₂ evolution was also observed. Perylene diimide derivatives used in this study have shown light harvesting capability similar to the tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate.     

Preparation and characterization of RuO<Subscript>2</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O/carbon aerogel composites for supercapacitors

A series of RuO₂ · xH₂O/carbon aerogel (CA) composite electrode materials was prepared by a chemical precipitation method. Ultrasonication was used to accelerate the chemical reaction and improve the dispersion of RuO₂ · xH₂O particles on the surface and the pores of the aerogel. The structure and morphology of the as-prepared composite were characterized by N₂ adsorption isotherm, X-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM). The results showed that the CA had a pearly network structure and the composites had a relatively high specific surface area and mesopore volume. The electrochemical performance of the composite electrodes was studied by cyclic voltammetry, galvanostatic charge/discharge measurements and electrochemical impedance measurements. The results indicated a substantial increase in the specific capacitance of the composite. Moreover, the utilization efficiency of RuO₂ · xH₂O was greatly improved by loading it on the conductive and porous CA due to a significant improvement in the inter-particle electronic conductivity and the extensive mesoporous network of the composites.     

Dehydrogenation of isobutane over Sn/Pt/Na-ZSM-5 catalysts: The effect of SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratio,amount and distribution of Pt nanoparticles on the catalytic behavior

Sn/Pt/Na-ZSM-5 was used as catalyst for the dehydrogenation of isobutane, and the effect of SiO₂/Al₂O₃ ratio and the dispersion of Pt nanoparticles on the conversion and product selectivity were studied under atmospheric pressure at 848 K. The catalysts were characterized by various techniques such as H₂ chemisorption, TEM, SEM, EDX, XRD, FT-IR, TG/DTG, elemental analysis by XRF and ICP techniques. Higher dispersion of Pt nanoparticles in the catalyst with SiO₂/Al₂O₃ ratio of 40 resulted in higher selectivity for isobutene.     

Effect of timing and duration of midseason aeration on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from irrigated lowland rice paddies in China

Midseason aeration (MSA) of rice paddy fields functions to mitigate CH₄ emission by a large margin, while simultaneously promoting N₂O emission. Alternation of timing and duration of MSA would affect CH₄ and N₂O emissions from intermittently irrigated rice paddies. A pot trial and a field experiment were conducted to study the effect of timing and duration of MSA on CH₄ and N₂O emissions from irrigated lowland rice paddy soils in China. Four different water regimes, i.e., early aeration, normal aeration (the same as the local practice in timing and duration of aeration), delayed aeration, and prolonged aeration, were adopted separately and compared with respect to global warming potential (GWP) of CH₄ and N₂O emissions and rice yields as well. Total emission of CH₄ from the rice fields ranged from 28.6 to 64.1 kg CH₄ ha⁻¹, while that of N₂O did from 1.71 to 6.30 kg N₂O–N ha⁻¹ during the study periods. Compared with the local practice, early aeration reduced CH₄ emission by 13.3–16.2% and increased N₂O emission by 19.1–68.8%, while delayed aeration reduced N₂O emission by 6.8–26.0% and increased CH₄ emission by 22.1–47.3%. The lowest GWP of CH₄ and N₂O emissions occurred in prolonged aeration treatment, however, rice grain yield was reduced by 15.3% in this condition when compared with normal practice. It was found in the experiments that midseason aeration starting around D 30 after rice transplanting, just like the local practice, would optimize rice yields while simultaneously limiting GWPs of CH₄ and N₂O emissions from irrigated lowland rice fields in China.     

Adsorption characteristics analysis of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript> in 13X zeolites by molecular simulation and N<Subscript>2</Subscript> adsorption experiment

The adsorption characteristics of CO₂ and N₂ in 13X zeolites have been studied by the molecular simulation and N₂ adsorption experiment. It is found that the simulation results by Dreiding force fields are in an agreement with the published data. The influence of the σ and ε parameters of O_Z and Na⁺ on the adsorption performance is discussed. Then the optimized force field parameters are obtained. Specific surface area (S _B ) is calculated by simulation and experiment. Its relative error is just only 4.3 %. Therefore, it is feasible that S _B of 13X zeolites is obtained by the simulation methods. Finally, the impacts of pressure and temperature on adsorption characteristics are investigated. At low pressure, CO₂ adsorption in 13X zeolites belongs to the surface adsorption. As the pressure increase, the partial multilayer adsorption appears along with the surface adsorption. N₂ adsorption in 13X zeolites is different from that of CO₂. At low temperature of 77 K, two primary peaks are caused by the surface adsorption and multilayer adsorption respectively regardless of pressure variation. When the temperature is 273 K, the energy distribution curve appears undulate at low pressures. Then it becomes stable with the pressure increase. The surface adsorption plays an important role at the relative high pressures. The results will help to provide the theory guide for the optimization of force field parameters of adsorbents, and it is very important significance to understand the adsorption performance of zeolites.     

Temperature programmed desorption of oxygen from Pd films interfaced with Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZrO<Subscript>2</Subscript>

The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y₂O₃–stabilized–ZrO₂ (YSZ), an O²⁻ conductor, under high-vacuum conditions and temperatures between 50 and 250 °C. Oxygen was adsorbed both via the gas phase and electrochemically, as O²⁻, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300 °C (state β₁) and 340–500 °C (state β₂). The creation of the low temperature peak is favored at high exposure times (exposure >1 kL) and low adsorption temperatures (T_ads < 200 °C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450 °C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O²⁻ pumping to the Pd catalyst film show two peaks (at 350 and 430 °C) corresponding to spillover O_ads and according to the reaction:

CO and CO<Subscript>2</Subscript> Methanation Over Ni/SiC and Ni/SiO<Subscript>2</Subscript> Catalysts

Ni/SiC and Ni/SiO₂ catalysts prepared by both wet impregnation (WI) and deposition–precipitation (DP) methods were compared for CO and CO₂ methanation. The prepared catalysts were characterized using N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), H₂ chemisorption, pulsed CO₂ chemisorption, temperature-programmed desorption of CO₂ (CO₂-TPD), transmission electron microscopy, and X-ray diffraction. H₂-TPR analysis revealed that the catalysts prepared by DP exhibit stronger interaction between the nickel oxides and support than those prepared by WI. The former catalysts exhibit higher Ni dispersions than the latter. The catalytic activities for both reactions over Ni/SiC and Ni/SiO₂ catalysts prepared by WI increase on increasing the Ni content from 10 to 20 wt%. The Ni/SiC catalyst prepared by DP shows higher catalytic activity for CO and CO₂ methanation than that of the Ni/SiC catalyst prepared by WI. Furthermore, it exhibits the highest catalytic activity for CO methanation among the tested catalysts. The high Ni dispersion achieved by the DP method and the high thermal conductivity enabled by SiC are beneficial for both CO and CO₂ methanation.