Effect Of Metal Loading Research Articles

Catalytic Carbon Monoxide Oxidation Over Copper/Silica Nanocatalysts

In this work, the catalytic activity of copper/silica nanocatalysts (prepared by incipient wetness impregnation of the metal salt on nanosilica, thermally extracted from rice husk) on the oxidation of carbon monoxide is investigated. The effect of metal loading on the physico-chemical features of the prepared catalysts has been investigated by X-ray diffraction, differential thermal analysis, transmission electron microscopy, nitrogen adsorption-desorption at −196°C, and temperature programmed reduction. The nanocatalyst loaded with 30.7 wt% CuO showed the highest surface area having newly created mesopores, with respect to the parent nanosilica. The temperature programmed reduction analysis indicated the presence of different types of copper species, including variation in their oxidation states, on the surface of the Cu20 and Cu30 catalysts. The catalytic activity on carbon monoxide oxidation at temperatures between 125 to 500°C was enhanced associated by increasing both copper oxide loading and the reaction temperature. The activity of the Cu30 catalyst at low temperatures attributed to the presence of the bulky cupric oxide species with a polar oriented (111) surface, which subsequently enhanced the catalyst surface adsorption efficiency; also, the presence of the cuprous oxide species can precede the carbon monoxide oxidation reaction through the associative (Langmuir-Hinshelwood) mechanism.

Effects of metal loading and support for supported cobalt catalyst

Several series of supported cobalt catalysts were synthesized with different loadings and supports. These catalysts were studied by in situ diffuse reflectance Fourier transformed infrared (DRIFT) spectroscopy during the CO2 hydrogenation reaction. The catalysts were also characterized by Ultraviolet visible near-infrared (UV–vis–NIR) spectroscopy and X-ray diffraction (XRD). The nature of interaction between cobalt and the support was determined by calcining the catalysts at elevated temperature and observing changes, if any, by UV–vis–NIR spectroscopy. The reduced catalysts did not possess cobalt oxide phases or cobalt-support compounds, except for the niobia supported cobalt catalyst, where cobalt niobate was readily formed. During reaction adsorbed CO and formate species were observed. The intensity and presence of the adsorbed species was dependent on the specific supported cobalt catalyst. The highest activity was observed for high loadings of cobalt supported on ceria followed by magnesia, alumina, zirconia, silica, titaina and niobia. At low loadings, however, ceria supported cobalt catalyst possessed a lower activity. Thus, the choice of the supports and the loading of the active metal are important while designing the supported cobalt catalysts.

Preparation and characterization of mesoporous silica supported cobalt oxide as a catalyst for the oxidation of cyclohexanol

Cobalt oxide catalysts supported on mesoporous silica SBA-15 were prepared by the “two-solvent” method and compared with analogous catalysts prepared by the more conventional methods of impregnation and adsorption. Cobalt nitrate was used as the precursor. The catalysts were characterized by N2 adsorption–desorption, XRD, FTIR, XPS, TPR, ICP-MS, TEM and DR UV–vis. Their activity for the oxidation of cyclohexanol was determined by GC and GC–MS. The effect of metal loading on the morphology and catalytic activity of the catalysts was investigated. The catalyst with the lowest cobalt content exhibited the highest catalytic activity for cyclohexanol oxidation due to the better accessibility of the reactants to the catalytic sites.

Electrooxidation of CO and methanol on well-characterized carbon supported PtxSn electrodes. Effect of crystal structure

The role of two intermetallic phases of PtSn, namely Pt3Sn (fcc phase) and PtSn (hcp phase) for the electrooxidation of CO and methanol has been evaluated. Carbon supported Pt3Sn and PtSn nanosized particles have been prepared by controlled surface reactions. The actual structure of the PtSn alloys has been evaluated and confirmed by means of XRD and HR-TEM studies which reveal the predominance of either the hcp or the fcc phase in each catalyst. The catalysts have been further characterized to identify the actual metal loading and Pt/Sn atomic ratio in order to eliminate particle size or metal loading effects on their electrocatalytic performance. The performance of the catalysts for the electrooxidation of CO and methanol has been evaluated by electrochemical techniques along with in situ techniques such as electrochemical coupled Infrared Reflection Absorption Spectroscopy (EC-IRAS) and differential electrochemical mass spectrometry (DEMS). Altogether, the results presented in this work reveal that Pt3Sn fcc is more active than PtSn hcp for the electrooxidation of CO and methanol and that the contribution of the hcp phase in those electrocatalytic processes is negligible.

Production of hydrogen via steam reforming of bio-oil over Ni-based catalysts: Effect of support

Nickel-based catalysts supported on zirconia (Ni/ZrO 2) were prepared, characterized and tested for the production of hydrogen via steam reforming of bio-oil. The effects of metal loading on the hydrogen (H 2) and carbon monoxide (CO) yields and the carbon deposition percentage were investigated. In order to examine the effect of support, the results obtained on zirconia support were compared to the results obtained over nickel-based catalysts supported on alumina (Ni/Al 2O 3). It was found that the Ni/ZrO 2 catalysts presented higher activity than those supported on alumina for hydrogen production. The CO yields obtained over Ni/ZrO 2 catalysts were also higher than those obtained over Ni/Al 2O 3 catalysts. A potential H 2 yield of almost 80% can be obtained at 850 °C using Ni/ZrO 2 catalysts with a nickel content of 14%; whereas, the H 2 yield was less when Ni/Al 2O 3 catalysts were employed. The amount of carbon deposited on each catalyst was measured. It was observed that the carbon depositions on the Ni/ZrO 2 catalysts were extremely high. A comparison between the amounts of carbon deposited on the Ni/Al 2O 3 and Ni/ZrO 2 catalysts revealed that the carbon deposition is strongly dependent on the type of support.

Deep desulfurization of diesel fuel by selective adsorption over Ni/Al2O3 and Ni/ZSM-5 extrudates

Adsorptive desulfurization using porous materials is based on the ability of a solid sorbent to selectively adsorb organic sulfur compounds from a refinery stream. In the present study, different sorbents were prepared by varying the Ni/Cu loadings onto ZSM-5 (Si/Al=20) and activated alumina for the removal of sulfur from commercial diesel fuel containing approximately 325ppmw total sulfur (S). To improve the adsorbent efficiency for sulfur removal, hydrogen peroxide was used as an oxidizing agent. The total sulfur in the sample was determined using X-ray fluorescence (XRF) analyzer. Effect of metal loading on sorption performance in the presence of H2O2 oxidant was investigated and compared on the basis of total sulfur removal, sorption capacity and adsorption breakthrough curves. Investigations revealed that sulfur removal strongly depends on the nature of metal, its amount and the nature of the support material. 10% Ni/Al2O3 adsorbent resulted in higher sulfur removal as compared to Ni/ZSM-5 and Cu/Al2O3 adsorbents. More than 90% removal of sulfur was observed with Ni/Al2O3 in presence of H2O2 oxidant. Fixed bed column experiments were carried out using Ni/Al2O3 and the performance of the column break through curves was investigated. Effect of flow rate, bed height and oxidizing agent was investigated in column experiments using 10% Ni/Al2O3. From the analysis of bed depth service time model the values of adsorption capacity and rate constant were found to be 496mgS/kg and 0.006 (mg/kg)−1h−1 respectively.

Towards understanding the microstructures and hydrocracking performance of sulfided Ni–W catalysts: Effect of metal loading

Detailed structural characterization of Ni–W hydrocracking catalysts with different metal loading were investigated before and after sulfidation by XRD, NH 3-TPD, TPR, XPS and HRTEM, then their catalytic performances were examined by hydrocracking of n-dodecane. Increasing metal amount would lead to the increase in sulfidation of W phase and Ni phase, WS 2 slab length and stacking WS 2, the metal–support interaction became weaker and the reducibility of catalyst was improved, therefore, catalytic activity increased and reached an optimum at about 30 wt.% total metal oxides. Further increase in the metal content would lead to the multiple layer metal distribution and increasing WS 2 slab length and slab stacking degree to a higher extent, which would result in the decrease of metal active site at edge and corner site of WS 2 slabs, and finally decrease the catalytic activity.

Modified dolomite in biomass gasification with simultaneous tar reformation and CO2 capture: effect of metal loading

The CO2 absorption capacity of calcined dolomite [a (CaMg)O solid solution] doped with iron and nickel transition metals has been investigated in a fixed bed reactor operating at temperature conditions (650°C) at which the sorption process is thermodynamically favoured at ambient pressure. The presence of metals (catalytic sites) between CaO grains (CO2 absorption sites) may improve the potential of dolomite for the simultaneous process of catalytic tar reforming and CO2 capture in biomass gasification, with the aim of developing an effective combined catalyst and sorbent particle. It was found that iron and nickel may be optimised in the substrate reducing critical limitations on CO2 capture capacity. A Sorption Enhanced Reforming test is proposed, at 650°C, for both iron and nickel doped calcined dolomite, using toluene as model tar compound: iron has been found to be not active in such conditions, whereas the 4% Ni/(CaMg)O has been indicated as the most suitable combined catalyst and sorbent particle.

Si/Al and metal loading effects on the templated synthesis of Ni nanowires in CAN and MOR zeolite frameworks

Zeolites with 1D pore channels, such as cancrinite (CAN) and mordenite (MOR), have the potential to be used as templates in the synthesis of subnanometre metal nanowires. Previous studies show a strong correlation between the location of Al atoms in zeolites and the positioning of the metal atoms inside the zeolite framework. Thus, Metropolis Monte Carlo simulations were used here to study the behaviour of Ni atoms within the CAN- and MOR-type zeolites at different Si/Al ratios and Ni loadings. It was found for both zeolite frameworks that a lower Si/Al ratio favoured energetically the positioning of Ni atoms in the 1D pore channels and that higher loadings of Ni promote the formation of 1D Ni structures. These results suggest that it is possible to use zeolites with the CAN and MOR frameworks and low Si/Al ratio as effective templates for the synthesis of metal nanowires.

Enhanced carbon adsorption treatment for removing cyanide from coking plant effluent

Batch experiments were conducted to determine the effects of metal loading and fixing methods on the capacity of granular activated carbon (GAC) for removing cyanide from KCN (pH 11), K3Fe(CN)6 solutions and several SCP effluent samples. KI fixed carbon (Cu/KI-GAC) was the most effective among the GAC samples tested. Adsorption was the primary mechanism of cyanide removal; catalytic oxidation of the adsorbed cyanide on carbon surface contributed a minor amount of the observed removal. Four small adsorbers containing the base GAC and 0–100% of Cu/KI-GAC were employed for treating a Fenton oxidized/precipitated SCP effluent sample. After the start-up period (<3-week) to establish the effective biological activated carbon (BAC) function in the adsorbers, the effluents became stable and met the discharge limits (CODCr<50mg/L and TCN<0.5mg/L); with >30% Cu/KI-GAC in the adsorber, the effluent would meet the discharge limits during the start-up phase.

Suppression of carbon formation in steam reforming of methane by addition of Co into Ni/ZrO2 catalysts

We investigated the steam reforming of methane (SRM) over various NiCo bimetallic catalysts supported on ZrO2 to determine whether the addition of Co on the Ni catalyst suppressed carbon formation. The effect of metal loading on SRM reaction was evaluated in a downflow tubular fixed-bed reactor under various steam-to-carbon (S/ C) ratios and temperatures. For monitoring changes in the catalysts before and after the SRM reactions, several tech- niques (BET, XRD, TEM, and CHN analysis) were used. The effects of reaction temperature, gas hourly space velocity (GHSV), and molar S/C ratios were studied in detail over the various catalyst combinations. It was found that an Ni- to-Co ratio of 50 : 50 supported on ZrO2 provided the best catalytic activity, along with an absence of coking, when operated at a temperature of 1,073 K, a GHSV of 24 L g −1 h −1 , and an S/C ratio of 3 : 1.

Metal loading effect on rare earth element binding to humic acid: Experimental and modelling evidence

The effect of metal loading on the binding of rare earth elements (REE) to humic acid (HA) was studied by combining ultrafiltration and Inductively Coupled Plasma Mass Spectrometry techniques. REE–HA complexation experiments were performed at pH 3 for REE/C molar ratios ranging from ca 4 × 10 −4 to 2.7 × 10 −2. Results show that the relative amount of REE bound to HA strongly increases with decreasing REE/C. A middle-REE (MREE) downward concavity is shown by patterns at high metal loading, whereas patterns at low metal loading display a regular increase from La to Lu. Humic Ion Model VI modelling are close to the experimental data variations, provided that (i) the ΔLK 2 parameter (i.e. the Model VI parameter taken into account the presence of strong but low density binding sites) is allowed to increase regularly from La to Lu (from 1.1 to 2.1) and (ii) the published log K MA values (i.e. the REE–HA binding constants specific to Model VI) are slightly modified, in particular with respect to heavy REE. Modelling approach provided evidence that log K d REE patterns with varying REE/C likely arises because REE binding to HA occurs through two types of binding sites in different density: (i) a few strong sites that preferentially complex the heavy REE and thus control the log K d REE atterns at low REE/C; (ii) a larger amount of weaker binding sites that preferentially complex the middle-REE and thus control the log K d REE pattern at high REE/C. Hence, metal loading exerts a major effect on HA-mediated REE binding, which could explain the diversity of published conditional constants for REE binding with HA. A literature survey suggests that the few strong sites activated at low REE/C could be multidentate carboxylic sites, or perhaps N-, or P-functional groups. Finally, an examination of the literature field data proposed that the described loading effect could account for much of the variation in REE patterns observed in natural organic-rich waters (DOC > 5 mg L −1 and 4 ⩽ pH ⩽ 7).

MIBK from acetone on Pd/H-[Ga]ZSM5 catalysts: Effect of metal loading

This work presents the preparation and characterization of three bifunctional catalysts consisting of palladium supported on H-[Ga]ZSM5 zeolite, with a Si/Ga atomic ratio of 16 and Pd contents of 0.09, 0.50 and 1.02 wt%. The lowest and highest Pd content solids, which were assessed by transmission electron microscopy (TEM), show dispersion of the supported phase of 90% and 73%, respectively. The XPS characterization studies of the catalysts allowed to detect the presence of framework, tetrahedral Ga species, Pd(0) aggregates and Pd(0) atomically dispersed. These solids were tested in the synthesis of methyl isobutyl ketone (MIBK) from acetone. The results confirm that the catalyst with 1.02 wt% Pd, shows an initial global activity about twice as higher as that of 0.09 wt%Pd/H-[Ga]ZSM5, and additionally the selectivity to MIBK of the former is four times higher. These results show that the catalyst with lower Pd content do not have a high number of active metallic sites to catalyze the hydrogenation of Mesityl oxide to MIBK, even though it showed an excellent dispersion, while the catalyst with 1.02 wt% Pd seems to be a catalyst with a proper balance of the acidic-hydrogenating functions.

π-Mode Stopband Characteristics Caused by Asymmetries of Support Rod and Loaded Metal in Helix Structures

A fully three-dimensional (3-D) helix traveling-wave tube (TWT) simulation model has been developed using a commercial electromagnetic (EM) finite-element-method (FEM) code. The model is used to simulate the π-mode stopband characteristics caused by asymmetries of support rods and metal loading in helix TWTs. Compared with the previous analytical method, the present simulation method can calculate the natural stopband of the π-mode, the absolute π-mode frequency, and the asymmetric effect of metal loading.

Selective CO methanation catalysts for fuel processing applications

Abstract Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst activity and selectivity. Even operating at a gas-hourly-space-velocity as high as 13,500 h −1 , a 3% Ru/Al 2 O 3 catalyst with a 34.2 nm crystallite was shown to be capable of reducing CO in a reformate to less than 100 ppm over a wide temperature range from 240 to 280 °C, while keeping hydrogen consumption below 10%. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H 2 and CO 2 .

Transition Metal Exchanged Zeolite Layers for Selectivity Enhancement of Metal-Oxide Semiconductor Gas Sensors

A novel method of improving the selectivity of metal oxide gas sensors has been developed by using catalytically active molecular sieve materials. They have been successfully introduced into a proprietary sensor array. The cracking patterns of linear alkanes over transition metal exchanged zeolite Y have been measured using a zeolite bed/GC/MS experimental set-up within a temperature range of 300degC to 400degC. Studies have been carried out regarding the effects of metal loading, zeolite type, material fabrication techniques, and operating temperature in relation to catalytic activity and selectivity. The composite sensors utilising the novel zeolite materials have been used in a custom built sensor rig that houses three dual electrode sensors and can measure real-time responses of these sensors to an introduced headspace generated from organic liquids

Effect of metal loading and carbon support microstructure on the dispersion of Pt/C catalysts prepared viaadsorption of chloroplatinic acid

Adsorption of H2PtCl6onto a carbon support followed by reduction of the adsorbed platinum species with H2at 250°C leads to Pt/C catalysts, which show universal volcano-like dependence of platinum dispersion on the metal loading in the range from 0.01 to 0.55mmol (Pt)/m2(SBET) when highly disordered carbons, namely, active carbons and carbon blacks, are used as supports. The maximal dispersion D(CO/Pt) = 0.8 is attained at 0.18mmol (Pt)/m2 (SBET). With other factors being equal, the dispersion of platinum supported on carbons with a more regular crystal structure, especially Sibunit-type supports, proves to be the highest and independent of the metal loading.The differences between the two groups of carbon supports are explained by the differences in the state of the adsorbed platinum precursors.

Effects of crystal structure on photolysis of H 2O on K–Ta mixed oxide

K–Ta mixed oxides with two different crystal structures, i.e. KTaO 3 and K 2Ta 2O 6, have been prepared by alkoxide and solid-state reaction routes. K 2Ta 2O 6 single phase with pyrocrhore like structure can be obtained by the alkoxide method, however, this phase cannot be obtained by a conventional solid-state reaction route. It was found that the prepared K 2Ta 2O 6 exhibits the higher activity to photolytic splitting of H 2O into H 2 than that of KTaO 3 which is reported as the active catalyst for the H 2O decomposition. Crystalline size of K 2Ta 2O 6 pseudo-pyrochlore oxide can be controlled by the hydrolysis condition for alkoxide. It was seen that the crystalline size has a large influence on the photocatalytic decomposition activity and the highest activity was obtained at the crystal size of 30 nm. Effects of metal loading were also investigated on K 2Ta 2O 6 oxide and among the examined metals, activity to photolysis of water increased by loading Rh. Formation of oxygen was also observed when 0.2 wt.% Rh was loaded.

Catalytic Combustion of Methane on Fe-TiO2 Catalysts Prepared by Sol-Gel Method

Two different series of titania-supported iron catalysts prepared by the sol-gel method have been characterised and tested in the combustion of methane at atmospheric pressure. In each series, the effect of metal loading (1, 5 and 10 wt%) and gelation pH (3 and 9) were studied. Characterisation data of calcined catalysts, carried out by specific area measurement, TPR, X-ray diffraction, XPS and EPR revealed no significant changes in metal dispersion. The catalytic activity of the solids were evaluated in the combustion of methane under stoichiometric mixture of CH4/O2 from 473 K up to the temperature required for total combustion. The best performance was shown by catalysts having 5 wt.%, which is ascribed to a balance of factors like the presence of a sufficient concentration of iron at the surface, achievement of relatively high dispersion state for iron and the presence of Fe+3 ions incorporated to the lattice of titania.

Highly enhanced photoreductive degradation of perchlorinated compounds on dye-sensitized metal/TiO2 under visible light.

This study reports an example of visible-light photocatalyst based on TiO2 modified by ruthenium-complex sensitizers and noble metal deposits. The photodegradation of trichloroacetate (TCA) and carbon tetrachloride was used as a probe reaction for evaluating the visible light activity of the photocatalyst under the illumination of lambda > 420 nm. Photodeposition of platinum nanoparticles on dye-sensitized TiO2 (Pt/TiO2/Ru(II)L3) drastically enhanced the degradation rate of TCA and CCl4. The visible light reactivity of Pt/TiO2/Ru(II)L3 was optimal with [Ru(II)L3] = 10 microM, [TiO2] = 0.5 g/L, and Pt loading of about 0.2 wt %. Although no electron donors to regenerate the oxidized Ru-sensitizers were added in the aqueous suspension, the photoreductive dechlorination of perchlorinated compounds proceeded far beyond the stoichiometric limit of the initial sensitizer concentration. Water acted as an electron donor to regenerate the sensitizer with a concurrent production of dioxygen. On the other hand, Pt/TiO2/Ru(II)L3 was completely inactive in the presence of dissolved oxygen and the in-situ generated dioxygen gradually decelerated the dechlorination rate. Conduction band electrons transferred to O2 in preference to CCl4 and TCA on Pt deposits. Other noble metals (Ag, Au, and Pd) deposited on TiO2 showed a better oxygen-tolerance but less visible-light reactivity than PtTiO2/Ru(II)L3. Effects of metal loading on the visible light activity and its implications for the efficientvisible-light photocatalyst development are discussed.