Metal Particle Size Distribution Research Articles

Particle size distribution and characteristics of heavy metals in road-deposited sediments from Beijing Olympic Park

Due to rapid urbanization and industrialization, heavy metals in road-deposited sediments (RDSs) of parks are emitted into the terrestrial, atmospheric, and water environment, and have a severe impact on residents' and tourists' health. To identify the distribution and characteristic of heavy metals in RDS and to assess the road environmental quality in Chinese parks, samples were collected from Beijing Olympic Park in the present study. The results indicated that particles with small grain size (<150μm) were the dominant fraction. The length of dry period was one of the main factors affecting the particle size distribution, as indicated by the variation of size fraction with the increase of dry days. The amount of heavy metal (i.e., Cu, Zn, Pb and Cd) content was the largest in particles with small size (<150μm) among all samples. Specifically, the percentage of Cu, Zn, Pb and Cd in these particles was 74.7%, 55.5%, 56.6% and 71.3%, respectively. Heavy metals adsorbed in sediments may mainly be contributed by road traffic emissions. The contamination levels of Pb and Cd were higher than Cu and Zn on the basis of the mean heavy metal contents. Specifically, the geoaccumulation index (Igeo) decreased in the order: Cd>Pb>Cu>Zn. This study analyzed the mobility of heavy metals in sediments using partial sequential extraction with the Tessier procedure. The results revealed that the apparent mobility and potential metal bioavailability of heavy metals in the sediments, based on the exchangeable and carbonate fractions, decreased in the order: Cd>Zn≈Pb>Cu.

Catalytic behaviour of four different supported noble metals in the crude glycerol oxidation

The activity of four different noble metals (Ag, Au, Pd and Pt) in the liquid phase oxidation of pure glycerol was confronted with the results obtained with a crude glycerol fraction, received from a large-scale biodiesel production plant. The catalysts were characterized by numerous techniques, giving insight into actual metal loading (elemental analysis by ICP and XRF), surface morphology (nitrogen absorption methods—BET and porosity), chemical state of both the support and the metal (XRD and XPS), and, finally, the metal particle size distribution (TEM microscopy). A good dispersion of totally reduced noble metal particles of a nanometric size (an average metal diameters were equal 3.5nm, 4.2nm, 4.7nm and 21.2nm for respectively Pd, Pt, Au and Ag) was accompanied with a comparable values of total metal loadings on the alumina support (from 0.95 and 0.96wt.% for Pt and Pd, up to 0.98 and 1.13wt.% for Au and Ag supported catalysts, respectively). In terms of initial reaction rate, the most active sample was the Au/Al2O3 catalyst, both using pure (12976molh−1molAu−1) or crude glycerol (1230molh−1molAu−1). However, comparison of the selectivities and conversions after 1–2h shows that the most robust and resistant catalyst – toward the impurities present in crude glycerol – is Pd/Al2O3, with a loss of conversion less than 50% (in respect to analogous reaction using pure glycerol) and almost unchanged high selectivity to glyceric acid (close to 80–90%). Ag/Al2O3 also showed a relatively high resistance to impurities in terms of glycerol conversion, but with a drastic modification of its selectivity. The activity of the two other catalysts was dramatically affected with a conversion divided by ca. 4 and even 10 for the Pt and the Au catalysts, respectively, when using crude glycerol instead of pure glycerol. Finally, the effect of each main impurity (MONG-NM, i.e., matter organic non-glycerol and non-methanol; ash; methanol; sulphur compounds) was independently studied. In any case, the sulphur compounds and MONG-NM were the impurities the most detrimental for the performances of catalysts. Thus, they should be removed in priority from crude glycerol fractions before reaction, while ashes and methanol should not be considered as completely undesirable.

폐 PCBs의 미분쇄 공정 적용에 따른 유가금속 분포 특성 및 금속 침출 향상에 관한 연구

The main objective of this study is to recovery valuable metals with metal particle size distributions in waste cell phone PCBs(Printed Circuit Boards) by means of pulverization and nitric acid process. The particle size classifier also was evaluated by specific metal contents. The PCBs were pulverized by a fine pulverizer. The particle sizes were classified by 5 different sizes which were PcS1(0.2 mm below), PcS2(0.20~0.51 mm), PcS3(0.51~1.09 mm), PcS4(1.09~2.00 mm) and PcS5(2.00 mm above). Non-magnetic metals in the grinding particles were separated by a hand magnetic. And then, Cu, Co and Ni were separated by 3M nitric acid. Particle diameter of PCBs were 0.388~0.402 mm after the fine pulverizer. The sorting coefficient were 0.403~0.481. The highest metal content in PcS1. And the bigger particle diameter, the lower the valuable metals exist. The recovery rate of the valuable metals increases in smaller particle diameter with same leaching conditions. For further work, it could improve to recovery of the valuable metals effectively by means of individual treatment, multistage leaching and different leaching solvents.

Preparation of Ag/Cu/Ti Nanofluids by Spark Discharge System and Its Control Parameters Study

This study selected silver, copper, and titanium as the research objects to explore the relationship between nanofluids properties and electrical discharge machining (EDM) processes. Regarding the products, UV-visible spectroscopy (UV-Vis) was applied to measure the concentration distribution of nanofluids; zeta-size analysis is applied for measuring nanometal particles’ Zeta-Potential and the size distribution of metallic particles in the fluid. Finally, various instruments, including scanning electron microscope (SEM), were applied to observe the shape, size, and composition ratio of metal particles after processing. According to the experimental results, the control of the discharge pulse time, in addition to affecting the concentration of metallic liquid and temperature in the process, affects the size of the metal particles after the process. As the resistivity of silver and copper is very low, at about15×10-9 Ω·m, ifTONis set to between 10~50 μs, good preparation efficiency can be obtained. The resistivity of titanium is420×10-9 Ω·m, which is much larger than that of silver or copper. Hence,TONshould be set to approximately 100 μs to achieve a good discharge success rate.

Improved bonding strength of bioactive cermet Cold Gas Spray coatings

The fabrication of cermet biocompatible coatings by means Cold Gas Spray (CGS) provides prosthesis with outstanding mechanical properties and the required composition for enhancing the bioactivity of prosthetic materials. In this study, hydroxyapatite/Titanium coatings were deposited by means of CGS technology onto titanium alloy substrates with the aim of building-up well-bonded homogeneous coatings. Powders were blended in different percentages and sprayed; as long as the amount of hydroxyapatite in the feedstock increased, the quality of the coating was reduced. Besides, the relation between the particle size distribution of ceramic and metallic particles is of significant consideration. Plastic deformation of titanium particles at the impact eased the anchoring of hard hydroxyapatite particles present at the top surface of the coating, which assures the looked-for interaction with the cells. Coatings were immersed in Hank's solution for 1, 4 and 7days; bonding strength value was above 60MPa even after 7days, which enhances common results of HAp coatings obtained by conventional thermal spray technologies.

Size Distribution Behavior of Metallic Iron Particles in Coal-Based Reduction Products of an Oolitic Iron Ore

The size distribution of metallic iron particles is important to better understand the coal-based reduction mechanisms of refractory iron ores. This study was focused on the particle size distribution behavior of metallic iron in coal-based reduction products of an oolitic iron ore. The size of metallic iron particles was measured using image analysis, and the data obtained were analyzed using frequency and cumulative distributions. The curves of the size-frequency distribution and cumulative passing percentage of metallic iron particles exhibited nearly the same trend with respect to particle size. The particle size distribution of metallic iron particles was markedly influenced by both reduction time and temperature. The number of metallic iron particles with large size increased with the reduction time and temperature. Goodness-of-fit tests indicated that the power function and the cumulative distribution function (CDF) of the log-normal distribution best fitted the experimental data of size frequency distribution and cumulative passing percentage of metallic iron particles, respectively.

Synthesis of Pt@Ni Core-Shell Nanoparticles Using Mwcnt's Supported for Oxygen Reduction Reaction

Multi-walled carbon nanotubes (MWCNTs) are nanostructures with unique physicochemical properties. MWCNTs can be obtained using different catalytic agents, being the most common the organometallic materials based on Fe. In this work, MWCNTs were produced using thermal chemical vapor deposition; MWCNTs surface was modified by nitric acid to introduce functional groups which act as anchors for metallic nanoparticles. On the other hand, the oxygen reduction reaction (ORR) in a tends to be the slowest reaction in a fuel cells, being this important issue to solve. It has been demonstrated that bimetallic catalysts (e.g. PtRu, PtCo, PtNi, etc.) are a good option for the ORR. The effect of the second metal helps the Pt, generating an improvement in the activity. Pt@Ni core-shell nanoparticles with different Pt/Ni ratios have been prepared by chemical reduction, supported onto MWCNTs and used as electrocatalysts for PEMFC. Chemical reduction allows the production of a very narrow size distribution of metal particles, with an average size around the 10 nm. The morphology of the electrocatalyst was characterized by XRD and HRTEM. It was found that the Pt@NiMWCNTs catalyst exhibited a core-shell nanostructure. The ORR on Pt@Ni core shell was studied using the rotating disk electrode (RDE) technique in an O2-saturated acid solution. A normal three electrode cell was used with the Pt@Ni/MWCNT as working electrode (deposited in glassy carbon), Ag/AgCl (KCl Sat) as reference, a Pt wire as counter electrode, and 0.5M H2SO4 as electrolyte. The results and discussion of the electrochemical studies will be discussed.

Particle size distribution of metallic iron during coal-based reduction of an oolitic iron ore

The objective of this study was to evaluate the effect of reduction temperature, reduction time and binary basicity on the size of metallic iron particles in coal-based reduction products of an oolitic iron ore. The particle size distribution behavior (i.e., cumulative passing percentage and mean size of metallic iron particles) during reduction was investigated in detail. Results showed that the particle size distribution of metallic iron particles was strongly influenced by reduction temperature, reduction time and binary basicity. The cumulative passing percentage and mean size significantly increased with reduction temperature and time in the entire range of the experiments. All curves of cumulative passing percentage versus particle size under different conditions demonstrated a similar trend (continuous increase). The size distribution parameters and mean size slightly increased with increasing binary basicity and significantly decreased when the binary basicity exceeded 1.0. The size of metallic iron particles could be controlled by adjusting the reduction conditions during coal-based reduction.

Comparative Study of Antibacterial Efficiency of M-TiO&lt;sub&gt;2&lt;/sub&gt; (M = Ag, Cu) Thin Films Grown by CVD

M-TiO2 (M = Ag, Cu) nanocomposite layers were grown by pulsed direct liquid injection chemical vapor deposition (DLICVD) on various substrates to produce bactericidal surfaces with long term activity. Monodisperse Ag nanoparticles (NPs) with an average size of 5-10 nm are embedded in an anatase matrix. A bactericidal behavior determined by the JIS Z 2801 standard test was found for Ag-TiO2 films for Ag ≤ 1 at. % and above. Higher Ag content is not necessary since efficiency is already at its maximum (relative activity 100%). By contrast, using Cu as antibacterial agent, a larger size distribution of metal particles was found (20 to 400 nm). Cu-TiO2 films exhibit a bactericidal behavior if their thickness is higher than 100 nm and Cu content ≥ 3.5 at. %. These coatings are still antibacterial after 5 months of aging and their efficiency has decreased by only 35%.

Source Characterization of Trace Elements in Indoor Environments at Urban, Rural and Roadside Sites in a Semi Arid Region of India

The present study investigated the particle size distribution of trace metals (Fe, Pb, Mn, Cu, Ni, Cr, Zn, Cd, Hg, and As) in the domestic environment, and examined the relationships among the levels of these metals and identified the related sources. Five homes at each site i.e., urban, rural and roadside, were selected for sampling. PM10 and PM2.5 samples were collected by using an APM-550 particulate sampler. Metals were analyzed by AAS after acid digestion. The monthly average PM2.5 concentration ranged from 80 to 184.67 µg/m3, while the PM10 monthly concentration ranged from 167.56 to 307.95 µg/m3. PM2.5 contributed 50–56% of PM10. The total contribution of the analyzed trace metals in PM2.5 was 6.2% while in PM10 it was 2.2%. This followed the order Fe > Zn > Pb > Cr > Ni > Cu > Mn. Pb and Ni exceeded the prescribed annual National Ambient Air Quality Standards (NAAQS) given by the Central Pollution Control Board (CPCB) by up to 5 and 36 times, respectively. For Pb and Ni it is 0.50 µg/m3 and 0.02 µg/m3, respectively. The particle mass was concentrated in the coarse size fraction, and the mass of individual trace metals was concentrated in finer sizes (except Fe), which is a major issue of concern. Intercorrelations and Principal Component Analysis were used to classify the two groups of sources, one from house dust and anthropogenic activities indoors, and the other from infiltration from outdoors. Enrichment factors with respect to outdoor metal concentrations have been identified for each metal. Fe was found to be totally contributed by outdoor dust. Mn and Cr are found to be less enriched, while Pb, Ni, Zn and Cu were found to have indoor sources.

Synthesis and characterization of ferrocenecarboxaldehyde immobilized on modified SiO2–Al2O3 in nanoscale, application for determination of penicillamine

In this study, we prepared a stable covalently bonded ferrocene derivative (ferrocenecarboxaldehyde) over SiO2–Al2O3 mixed-oxide in nanoscale size (Fe ions did not accumulate and were dispersed as Fe metal ion–nanoparticles). SiO2–Al2O3 mixed-oxide was functionalized with 3-aminopropyl-triethoxysilane group and ferrocenecarboxaldehyde was covalently linked to the organo-functionalized SiO2–Al2O3 mixed-oxide. Fourier transform infrared spectroscopy, UV–Vis, CHN elemental analysis, inductively coupled plasma optical emission spectroscopy (ICP–OES), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and cyclic voltammetry were used to characterize the synthesized materials. Nitrogen sorption measurements of the modified Si/Al mixed-oxide confirm the presence of the ferrocene molecules attached to the modified Si/Al mixed-oxide. The considerable decrease in the specific surface area clearly indicates functionalization of the surface of the mixed-oxide with ferrocene. The nitrogen and Fe contents of the organometallic-modified Si/Al mixed-oxide (SAPFE) were determined by elemental analysis and ICP–OES, respectively, which were then used to compute the immobilized SAPFE content. SEM and TEM images confirm that the metal particle (Fe ions) size distribution forms a continuum between the minimal (2–5 nm) and the maximal (about 50 nm) diameters. The organo-functionalized SiO2–Al2O3 mixed-oxide was used as a mediator for the determination of penicillamine at pH 6.0. Under the optimum conditions at pH 6.0, the oxidation peak potential of penicillamine at the modified electrode shifts about 400 mV to less positive value than for the unmodified carbon paste electrode. Differential pulse voltammetry exhibited two wide linear dynamic ranges of 0.06–7.5 and 7.5–140 μmol L−1 penicillamine. The detection limit was found to be 0.01 μmol L−1 penicillamine. Kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant were also determined using the electrochemical approaches. Finally, the modified electrode was used as a novel nanosensor for the determination of penicillamine in real samples such as drug, serum, and urine.

Metal concentration and particle size distribution of stream and river water polluted from copper rolling mill industry

Concentrations of heavy metals, pH, and particle size distribution parameters were measured in Dragica stream and Djetinja River water receiving wastewaters from copper rolling mill industry, Sevojno. The concen- trations of copper, zinc, lead, and mercury were determined for water samples collected in summer 2009. It was found that Copper Rolling Mill Sevojno was the significant source of water pollution with copper and zinc. Consider- ing that copper rolling mill industry, one of the larger emitters of sulfur dioxide, pollutes the area, the water pH was surprisingly alkaline. The particle size analysis results showed that particles from oil-in-water emulsion evidently got into stream water in spite of the purification devices used. In order to assess the possible relations between the measured parameters, a correlation analysis was per- formed. The correlation analysis showed a significant positive correlation between the total metal concentrations of copper and zinc, as well as between particle size dis- tribution parameters and the concentration of lead and copper.

Effect of preparation method on the performance of the Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part II-characterization

In the first part of this paper [1], we have discussed the effect of preparation method on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol (EtOH). One catalyst was synthesized using a sol–gel method (SG). The other was synthesized by adding nickel nitrate to a solution combustion synthesized alumina support (SCS). Based on the product distribution, we proposed the reaction pathway as a mixture of dehydrogenation of EtOH to acetaldehyde followed by C–C bond breaking to produce CO and CH4 and oxidation of acetaldehyde to acetic acid followed by decarbonylation to CO2 and CH4. CH4 (C2H6 and C3H8 also) can form via Fischer–Tropsch reactions of CO/CO2 with H2. The CH4 (C2H6 and C3H8) reacts to form hydrogen and carbon monoxide through steam reforming, while CO converts to CO2 mostly through the water-gas shift reaction (WGSR). The SG catalysts showed poorer WGSR activity than the SCS catalysts. The difference of the metal particle size distribution governed by preparation method appeared to be the key factor of controlling catalytic efficiency, but some contradictory results could not be explained.In this paper, we report the microstructural and phase compositional differences of the catalysts imposed by the variation of the preparation methods. The XRD analysis, TEM characterization, and H2-pulse chemisorptions showed that the SG samples sintered and metal particles grew during heat treatment and catalytic reaction, but for the SCS samples these changes are much less severe under similar conditions. N2 adsorption/desorption analysis showed that the used SCS(10%) catalyst contained a mesoporous structure of higher pore volume and the SG(%10) catalyst contained macro pores of smaller pore volume. The X-ray photoelectron spectroscopy (XPS) analysis of the used samples demonstrated less coke deposition and less bulk spinel formation on the SCS(10%) sample than that on the SG(10%) sample. These factors may be responsible for higher water gas shift activity in the SCS(10%) sample than that in the SG(%10) catalyst. For the CM(10%) sample, the large particle size and low dispersion of metal on the support were responsible for lower EtOH conversion, H2 & CO2 selectivity, and TOF values. Additionally, the XPS data showed that the SCS(2%) and SG(2%) catalysts have more bulk spinel than the 10% Ni samples and for SCS(2%) sample this is the highest. This diminishes the advantages of smaller Ni particle sizes and less C deposition for them, and explains the apparently anomalous kinetic results observed in the first part of the paper.

A new strategy for pressed powder eye shadow analysis: Allergenic metal ion content and particle size distribution

Nine cheap eye shadow products were analyzed through graphite furnace atomic absorption spectrometry (GF-AAS) to quantify their Cr, Co and Ni contents, all known to be skin sensitizers. In many cases, the concentrations were higher than 1 or 5ppm (μg/g), i.e. the limits recommended in the scientific literature to minimize the risk of reaction in particularly sensitive subjects. In most cases, the concentration of Cr was higher than that of Ni and Co, up to a limit case of 150mg/g. In this particular sample, the potential amount of Cr that could be released in ionic form was determined in sweat simulating solutions by GF-AAS and confirmed through a specific spectrofluorimetric method; the results indicated the presence of approximately 80–90ppb (ng/g) of Cr3+.The water dispersible particles were isolated from the eye shadow powders through a simple solvent extraction procedure. The aqueous suspensions were then sorted through sedimentation field flow fractionation (SdFFF) and the particles sizes were calculated from experimental fractograms using theory. For the most part, the computed sizes were in the micron range, as confirmed by some SEM photographs taken on fractions collected during the separations. The SdFFF coupled off-line with the GFAAS enabled elemental characterization of pigment particles as a function of size. This finding reduces the concern that the ingredients of such makeup formulations may contain nanoparticles.

MCM-41 supported Co[sbnd]Mo bimetallic catalysts for enhanced hydrogen production by ammonia decomposition

MCM-41 supported Co, Mo and CoMo bimetallic catalysts with different Co/Mo atomic ratios were prepared by incipient wetness impregnation, and the channels of MCM-41 acted as nano-reactor. The catalysts without pre-nitridation treatments were directly used to catalyze ammonia decomposition. The characterization of the catalysts was carried out by N2 physisorption, H2-TPR, Raman, XRD, TEM and XPS. The results show that the catalysts have the similar size distribution of metallic particles. Due to the synergistic effect between Co and Mo, MCM-41 supported CoMo bimetallic catalysts show higher ammonia decomposition activity compared to Co or Mo alone. The CoMo bimetallic catalyst with the Co/Mo atomic ratio of about 7/3 exhibits the highest NH3 conversion. Moreover, the Co7Mo3/MCM-41 catalyst shows good thermal stability.

Effect of preparation methods on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part I-catalytic activity

The effect of preparation method on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol (EtOH) has been investigated. The first catalyst was prepared by a sol–gel (SG) method and for the second one the Al2O3 support was made by a solution combustion synthesis (SCS) route and then the metal was loaded by standard wet impregnation. The catalytic activity of these catalysts of different Ni loading was compared with a commercial Al2O3 supported Ni catalyst [CM (10%)] at different temperatures, pressures, feed flow rates, and feed concentrations. Based on the product distribution, the proposed reaction pathway is a mixture of dehydrogenation of EtOH to CH3CHO followed by C–C bond breaking to produce CO + CH4 and oxidation of CH3CHO to CH3COOH followed by decarbonylation to CO2 + CH4. CH4(C2H6 and C3H8) also can form via Fischer–Tropsch reactions of CO/CO2 with H2. The CH4 (C2H6 and C3H8) reacts to form hydrogen and carbon monoxide through steam reforming, while CO converts to CO2 mostly through the water–gas shift reaction (WGSR). SG catalysts showed poorer WGSR activity than the SCS catalysts. The activation energies for H2 and CO2 production were 153, 155 and 167 kJ/mol and 158, 160 and 169 kJ/mol for SCS (10%), SG (10%), and CM (10%) samples, respectively.Primarily, the difference in the metal particle size distribution governed by the preparation method appeared to be the key factor controlling catalytic efficiency. The SCS samples (with smaller Ni particle size) turned out to be superior for EtOH conversion, selectivity for H2 & CO2, and TOF values of H2 and CO2 to the corresponding SG (10%), SG (5%) and CM (10%) samples of bigger Ni particles size irrespective of the reaction conditions. For the SG catalysts, the selectivity to CO increased with temperature, while SCS catalysts produced no CO. While the particle sizes of SCS (10%) and SG (2%) are almost the same and their selectivity to H2 and CO2 are close, the TOF values to H2 and CO2 production for the SG (2%) catalyst are 2–3 times lower than that of the SCS (10%) catalyst. Similarly, the Ni particle size on SCS (10%) is 2.5 times larger than that on SCS (2%), but their selectivity to H2 and CO2 are almost the same. These anomalous results can be explained by the microstructural and phase compositional differences of the catalysts imposed by the variation of the preparation methods and will be discussed in detail in part II of this paper.

Regard for particle size distribution in a model of the macrokinetics of the reduction of oxygen dissolved in water by a metal-ion-exchanger nanocomposite

The function of granulometric size distribution of metal particles is introduced into the equations of a mathematical model that describes the reduction of molecular oxygen from water by metal-ionexchanger nanocomposites. It is shown that the pattern and parameters of the distribution function have an effect on the behavior of the kinetic curve. It is noted that this is particularly important for systems in which small particles dominate. The calculation and analysis of changes in the metal particle size distribution curve during the process are performed using the example of a silver-sulfocation exchanger nanocomposite.

Methane dry reforming with CO 2 on CeZr-oxide supported Ni, NiRh and NiCo catalysts prepared by sol–gel technique: Relationship between activity and coke formation

Ni, NiRh and NiCo catalysts supported on Ce–Zr-oxide synthesised by pseudo sol–gel method have been investigated. Monometallic samples were performed with two different Ce/Zr ratios and by conventional impregnation. BET, XPS, TPR, TPO and TEM were applied for sample characterization and dry reforming of methane was carried out with a feed mixture consisted of CH 4/CO 2/Ar = 10/10/80 or CH 4/CO 2 = 70/30 ratio. Co and Rh containing samples were proved to be stable catalysts, the impregnated Ni catalyst only slightly, while sol–gel Ni samples slowly deactivated during the long term overnight run. The amount of carbon on the sample's surface after catalytic runs varied between 1 and 12 mg C/100 mg of catalyst. The Ni samples prepared by sol–gel and impregnation method had a peak maximum in TPO at 400 °C and 600 °C, respectively. In the case of bimetallic sol–gel samples the carbon that gave TPO peak at 360 °C was slowly transformed to that at 600 °C, showing that after several carbon deposition (dry reforming) and gasification (TPO) cycles structural changes in the catalyst and in the carbon morphology take place and graphitic carbon and nanotube formation become prevailing as was detected by TEM. Upon high temperature pre-treatment and methane dry reforming reaction, alloyed NiRh, NiCo particles and sintered Ni were observed, with the simultaneous presence of carbidic carbon, carbon nanotubes and shell-type graphitic carbon deposition. Support degradation and segregation happened to some extent, but still there was a certain amount of Ni in strong interaction with the support probably still included in the oxide matrix. Broad metal particle size distribution seems to play a role in long term stability. When pure methane was decomposed on Ni catalyst prepared by sol–gel method, the carbonaceous deposit could completely be removed by the subsequent CO 2 treatment, emphasizing the active role of Ce–Zr mixed oxide support in gasification of surface coke.

Surface-functionalized TUD-1 mesoporous molecular sieve supported palladium for solvent-free aerobic oxidation of benzyl alcohol

Palladium catalysts supported on TUD-1 mesoporous molecular sieves functionalized with various organosilanes were successfully prepared using a post-synthesis grafting method combined with a metal adsorption–reduction procedure. The correlation between catalyst structure, surface chemistry, metal loading, and catalytic activity was explored in the solvent-free selective oxidation of benzyl alcohol using molecular oxygen. TUD-1 outperformed other mesoporous silicas due to its unique open 3-D sponge-like mesostructure, which can effectively confine Pd nanoparticles and suppress the mass diffusion resistance. The type and content of grafted functional groups greatly affected the catalytic performance by tuning the surface basicity, metal particle size and size distribution, and metal–support interaction. 3-Aminopropyl triethoxysilane functionalization displayed the largest improvement in catalytic activity, showing a dramatically high quasi-turnover frequency of 18,571 h −1 for benzyl alcohol conversion.

Gas phase hydrogenation of nitroarenes: A comparison of the catalytic action of titania supported gold and silver

We have examined the catalytic action of 1 mol% Au/TiO 2 and Ag/TiO 2 in the continuous gas phase hydrogenation of a series of para-substituted (–H, –OH, –OCH 3, –CH 3, –Cl and –NO 2) nitroarenes. Both catalysts promoted exclusive –NO 2 group reduction, resulting in the sole formation of the corresponding amino-compound. The catalysts have been characterized in terms of temperature-programmed reduction (TPR), H 2 chemisorption, BET area, diffuse reflectance UV–vis, X-ray diffraction and HRTEM measurements. The formation of zero valent Au and Ag is established post-TPR. Au/TiO 2 showed a narrower metal particle size (1–10 nm) distribution than Ag/TiO 2 (1–15 nm) but both catalysts exhibited a similar surface area weighted mean size (6–7 nm). A time-invariant nitroarene conversion has been established where Au/TiO 2 delivered higher specific hydrogenation rates. We associate this response to an enhanced reactant activation on Au/TiO 2 to generate a negatively charged intermediate, consistent with a nucleophilic mechanism. The presence of electron-withdrawing substituents is shown to enhance –NO 2 reduction rate. This effect is quantified in terms of the Hammett relationship where a linear correlation between the substituent constant ( σ i ) and rate is established and a higher reaction constant ( ρ) was recorded for Au/TiO 2 (0.93) relative to Ag/TiO 2 (0.22). The data generated provide the first direct comparison of the catalytic action of supported Au and Ag in the hydrogenation of substituted nitroarenes and establish the viability of both catalysts to promote selective –NO 2 group reduction.