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A transient single-site kinetic model consisting of NH3-SCR (selective catalytic reduction) related reactions (NH3 adsorption/desorption, NH3 oxidation, NO oxidation, standard SCR, fast SCR, NO2-SCR, NH4NO3, and N2O formation) on a commercial multi-site Cu-Chabazite washcoated monolith was developed using laboratory scale synthetic gas bench (SGB) data and its potential towards predicting the downstream NOx concentrations was assessed using SGB and dynamometer tests. Kinetic model described the transient and steady-state data obtained for the model development in the SGB well. Single-site nature of the model enabled the prediction of the reactivity of the lower temperature active Cu site much better than the activity associated with higher temperature Cu sites. Validation experiments in the SGB at 185 °C which consisted of varying NH3 and NO2/NOx ratios were very well predicted. The kinetic model was also successful in predicting the instantaneous NOx emissions and cumulative NOx and N2O amount released in real-size SCR reactors during World Harmonic Transient Cycle (WHTC) in the 220–290 °C range. Model was in slight disagreement with measured cumulative NO but was in good in agreement with NO2 for the World Harmonic Stationary Cycle (WHSC) tests in dynamometer and 235–339 °C range, respectively. The developed model was found sufficient for both design and calibration of aftertreatment systems (ATS).

PtCu- and PdCu–mordenite allow for isothermal reaction at 200 °C for the stepwise methane to methanol conversion with comparably high yields. In contrast to traditional Cu-zeolites, these materials are more reactive under isothermal conditions than after high temperature activation., Chemical Science, 10 (1), ISSN:2041-6520, ISSN:2041-6539

A new technique termed Supercritical Ion Exchange (SCIE) was developed and used to synthesize Cu-mordenite (Cu-MORS). The ion exchange takes place between the Cu complex (Copper(II)trifluoroacetylacetonate) dissolved in supercritical CO2 (scCO2) and the extraframework protons in mordenite zeolite without requiring an aqueous phase. The occurrence of the ion exchange reaction was demonstrated by using 1H NMR analysis of the high-pressure fluid phase samples and by visual inspection of the fluid phase color change during the synthesis. SCIE resulted in selective ion-exchange inferred by the equilibrium isotherm. The prepared catalysts were used for the stepwise direct methane to methanol (sDMTM) process and results showed that methanol productivity increased linearly with increasing Cu loading up to a certain Cu wt%. Cu-MORS displayed 16% higher methanol productivity as compared to Cu-MORA (prepared by aqueous ion exchange) with the same Cu loading. The results demonstrated the importance of site selective ion-exchange for zeolite catalysis.

A unified transient kinetic model which can predict the adsorption, desorption and oxidation kinetics of NH3 over hydrothermally aged Cu-chabazite was developed. The model takes into account the variation of fractional coverages of NH3 storage sites due to hydrothermal aging. In order to determine the fractional coverage of these sites, the catalyst was aged for various times at a certain temperature followed by NH3 adsorption, desorption and temperature-programmed desorption (TPD) experiments. TPD profiles were deconvoluted mainly into three peaks with centres at 317, 456 and 526 oC, respectively. Hydrothermal aging resulted in the progressive increase in the intensity of the peak at 317 oC and decrease in the intensity of the peaks at 456 and 526 oC, along with decreased NH3 oxidation at high temperatures. A model for hydrothermal aging kinetics of the fractional coverage of storage sites was developed using three reactions with appropriate rate expressions with parameters regressed from experimental data. The model was then incorporated into a multi-site kinetic model for the degreened Cu-Chabazite by the addition of aging reactions on each storage site. The effects of both aging time and temperature on the kinetics NH3 adsorption, desorption and oxidation were successfully predicted in the 155-540 oC range. This study is the first step towards the development of a hydrothermal aging-unified kinetic model of NH3-Selective Catalytic Reduction over Cu-chabazite., Ford Otomotiv Sanayi A.Ş.

Aerogels are a unique class of materials due to their low density, high porosity, high surface area, and an open and interconnected pore structure. Aerogels can be organic, inorganic and hybrid with a plethora of surface chemistries. Aerogel-based products for thermal insulation are already in the market and many studies are being conducted in many laboratories around the world to develop aerogel-based products for other applications including catalysis, adsorption, separations, and drug delivery. On the other hand, bimetallic nanoparticles dispersed on high surface area carriers, which have superior properties compared to their monometallic counterparts, are used or are in development for a wide variety of applications in catalysis, optics, sensing, detection, and medicine. Investigations on using aerogels as high surface area carriers for dispersing bimetallic nanoparticles are leading to development of new composite materials with outstanding properties due to the remarkable properties of aerogels. The review focuses on the techniques to synthesize these materials, their properties, the techniques to tune their pore properties and surface chemistry and the applications of these materials.

Pt/Al2O3 and bimetallic PtPd/Al2O3 catalysts were prepared via supercritical deposition method using supercritical carbon dioxide. The effects of Pt loading of Pt/Al2O3 and Pd addition to Pt/Al2O3 on particle size, particle size distribution (PSD) and activity for NO and C3H6 oxidation and C3H6-selective catalytic reduction (C3H6-SCR) were investigated. Pt/Al2O3 catalysts were prepared with Pt loadings of 0.6, 1.2 and 2.1 wt% and a bimetallic PtPd/Al2O3 catalyst was prepared with total metal loading of 1.4 wt% and Pt:Pd molar ratio of 1.3:1. A small fraction of the particles agglomerated after calcination at 550 °C. Around 98 % of the particles had an average particle size of ?1 nm. The rest of the particles were larger and average size of these larger particles was ?10 nm for monometallic catalysts and ?6.5 nm for PtPd/Al2O3. All catalysts were found to be active for NO and C3H6 oxidation and C3H6-SCR reactions. NO oxidation performance of 1.2 wt% Pt/Al2O3 catalyst was the highest. C3H6 oxidation activity increased with increasing metal content. Light-off temperature for C3H6 oxidation shifted to higher temperature in the presence of NO, suggesting competitive oxidation of C3H6 and NO. Concentration profiles indicated that C3H6-SCR started when C3H6 conversion by oxidation reached 50 %; C3H6 was consumed both by oxidation and C3H6-SCR at higher conversions., Ford Otosan A.Ş.

Cu supported on SiO2 can be used to directly convert methane to methanol in a stepwise process with no intrinsic need for a zeolite support. Effects of parameters such as the O-2 activation temperature, activation time, CH4 reaction temperature, CH4 partial pressure (pCH(4)), and Cu wt % on methanol yield were investigated. Increasing the O-2 activation temperature in the 200-800 degrees C range significantly improved the methanol yield, and when carried out at 800 degrees C, a methanol yield of 11.5 mu mol/g(ctalyst) was obtained after reaction with methane at 200 degrees C for the sample with 2 wt % Cu. Yield per mole of Cu increased exponentially from 1.0 to 59.1 mmol with decreased Cu wt % from 30 to 1, respectively. The increase in the O-2 activation time also strongly influenced the yield which corresponded to the increase in yield by a factor of >2 between 1 and 8 h. Increasing PCH4 from 0.05 to 1 atm resulted in a 5-fold increase in yield after activation at 450 degrees C; however, it resulted in at least 20% lower yields after activation at 800 degrees C showing that active sites of different nature were formed at different activation temperatures. The increase in yield with ramped O-2 activation temperature correlated with the dehydration of the samples as evidenced by X-ray absorption near-edge spectroscopy (XANES) and via mass spectroscopy (MS) traces of H2O during the O-2 activation step., Turkish Scientific and Technological Research Council (Scientific and Technological Research Council of Turkey (TÜBİTAK))

Kinetic models of NH3-SCR of NO based on modified redox (MR) and modified Eley-Rideal (ER) mechanisms calibrated using monoliths with Vanadia based washcoats with different thicknesses were cross compared. Both models were satisfactory for the washcoat thicknesses investigated at steady conditions in 120–540 °C range. MR mechanism better represented NO transients at 192 °C. Dependence of limiting regions on the washcoat thickness was determined via the analysis of washcoat concentration profiles and the concentration ratios of the fluid, fluid-washcoat interface and washcoat. Both models generally agreed with the borders of the limiting regions. During Standard SCR, the limits of the kinetic regime was below 309 and 271 °C for thinner and thicker washcoats, respectively. This was followed by mixed limitation regime upto 488 °C at the reactor entrance. Above 488 °C, transition to kinetically controlled regime was observed at the center of the monolithic reactors.

Excess CO2 adsorption isotherms on silica, resorcinol-formaldehyde, carbon, and wheat starch aerogels at 308 K, 318 K, and 328 K and at pressures up to 35 bar were measured using a volumetric method. Total or absolute adsorption isotherms were calculated from experimentally obtained excess adsorption isotherms using the pore volume of each adsorbent. It was found that silica aerogel with the BET surface area of 1158 m2 g−1 had a maximum absolute uptake of 14 mmol g−1 and resorcinol-formaldehyde aerogel (RFA-19) with the BET surface area of 620 m2 g−1 had a maximum uptake of 13 mmol g−1 at 308 K and 35 bar. CO2 adsorption isotherms for silica, resorcinol-formaldehyde, and wheat starch aerogels were well represented with the Langmuir model whereas isotherms for carbon aerogel were fitted with the Freundlich model. It was also found that the excess uptake correlated well with the mesopore surface area of each aerogel at various pressures. The isosteric heat of adorption for each aerogel was also determined from the variation of pressure with temperature at a constant excess uptake. Among all aerogels, wheat starch aerogel had the highest value of −32.1 kJ mol−1 and carbon aerogel had the lowest value of −17.7 kJ mol−1. Adsorption capacities of aerogels determined were comparable with other classes of adsorbents and presents an opportunity for further investigation of aerogels as potential materials for carbon capture especially at high pressures.

Mesoporous graphene aerogel (GA) supported Pt nanoparticles with narrow size distribution were prepared via supercritical deposition (SCD) using supercritical CO 2 (scCO 2 ). Pt(cod)me 2 precursor was dissolved in scCO 2 and adsorbed onto GA at 35 °C and 10.7 MPa. The Pt precursor was converted to its metal form under atmospheric pressure at various temperatures. The effects of precursor conversion temperature (400, 600, and 800 °C) on the structural properties of the composites were investigated using Raman Spectroscopy, XRD, XPS, and TEM. The average particle size increased from 1.2 to 2.9 nm when the conversion temperature was increased from 400 to 800 °C. The electrocatalytic activity of the samples towards the Oxygen Reduction Reaction were evaluated using cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements. SCD helped to preserve the textural properties of the GA after the Pt nanoparticle deposition, and thus Pt/GA converted at 600 °C exhibited an enhanced mass activity of 30.6 mA mg Pt −1 , outperforming the mass activities reported in the literature for Pt/GA electrocatalysts prepared using conventional routes.

Nanomaterials consisting of Ru nanoparticles dispersed in polydimethylsiloxane films were synthesized by supercritical deposition. The films were impregnated with the organometallic precursor bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (1,5-cyclooctadiene) ruthenium (II) under thermodynamic control in the presence of supercritical carbon dioxide (scCO 2 ) at 40 °C and 10.34 MPa. The precursor molecules were then converted to metallic Ru by thermal treatment in flowing N 2 at ambient pressure, resulting in well-dispersed nanoparticles with diameters of ≈2 nm.

Direct partial oxidation of methane into methanol is a cornerstone of catalysis. The stepped conversion of methane into methanol currently involves activation at high temperature and reaction with methane at decreased temperature, which limits applicability of the technique. The first implementation of copper-containing zeolites in the production of methanol directly from methane is reported, using molecular oxygen under isothermal conditions at 200 degrees C. Copper-exchanged zeolite is activated with oxygen, reacts with methane, and is subsequently extracted with steam in a repeated cyclic process. Methanol yield increases with methane pressure, enabling reactivity with less reactive oxidized copper species. It is possible to produce methanol over catalysts that were inactive in prior state of the art systems. Characterization of the activated catalyst at low temperature revealed that the active sites are small clusters of copper, and not necessarily di- or tricopper sites, indicating that catalysts can be designed with greater flexibility than formerly proposed.

Copper mordenite was used for the conversion of methane to methanol in a cyclic operation. Repeated cycling was possible using catalysts having different loadings prepared via aqueous ion exchange using copper(II) acetate (Cu-MORA) and solid state ion exchange using copper(I) chloride (Cu-MORS). For Cu-MORA, the yield increased by at least 30% on the second cycle and remained constant afterwards. Linear combination fitting of the XANES identified a similar increase in the fraction of CuI formed upon reacting with methane on the second cycle. For Cu-MORS residual chlorine initially hindered the production of methanol. Successive cycles removed chlorine and yielded significantly more methanol per copper than Cu-MORA. Over successive cycles of Cu-MORS, the fraction of the CuII species that was reduced to CuI upon reacting with methane correlated well with the amount of methanol produced. Although commonly done, analyzing only one reaction cycle is not representative of the long-term performance of methane to methanol over copper mordenite. Copper species equilibrate with cycling.

Supercritical fluid-based technologies are increasingly being used to develop novel functional nanostructured materials or improve the properties of existing ones. Among these, supercritical deposition (SCD) is an emerging technique to incorporate metals on supports. It has been used to deposit a wide variety of single or multi-metallic morphologies such as highly dispersed species, nanoparticles, nanorods and conformal films on high surface area supports, polymers and crystalline substrates. SCD is also attracting increasing attention for preparation of micro or nano-architectured functional materials in a highly controllable manner for electrochemical energy conversion and storage systems. Increasing number of studies in the literature demonstrates that materials synthesized using SCD are comparable or superior in performance as compared to their conventional counterparts. In this review, an overview of the fundamentals of the SCD technique is presented. Properties of a wide variety of nanostructured functional materials such as supported nanoparticles and films prepared using SCD for electrochemical applications are summarized. The electrochemical performance of these materials in electrochemical tests and also in fuel cells, electrolyzers and Li-ion batteries are also presented.

Mesoporous carbon aerogel (CA) supported PtCu bimetallic nanoparticles were prepared via a sequential supercritical deposition (SCD) method using supercritical carbon dioxide (scCO(2)). The effects of deposition order of the metal, annealing temperature and metal composition on the average PtCu particle size, size distribution and dispersion were investigated. Four sets of PtCu/CA samples were prepared with two Pt:Cu molar ratios (1:1 and 1:3) and with two different deposition orders (i.e. either Pt or Cu first). X-ray diffraction and electron microscopy data showed that all of the as-prepared samples formed homogeneously distributed disordered PtCu alloy nanoparticles with narrow particle size distributions on the CA support. Increasing annealing temperature in the range 600-950 degrees C increased the average particle size from 1.8 nm to 4.5 nm and resulted in the elimination of separate Cu nanoparticles on the CA surface. The dealloying of the supported PtCu nanoparticles were carried out by cyclic voltammetry and the activity of the dealloyed nanoparticles (after 300 potential cycles) towards the oxygen reduction reaction (ORR) was investigated using rotating disc electrode (RDE) experiments. During dealloying, peaks associated with bulk dissolution and deposition of Cu and dissolution and re-deposition of Cu from the alloyed PtCu nanoparticles were observed at initial cycles along with peaks associated with creation of new Pt sites. Supported nanoparticles with Pt: Cu molar ratios of 1:1 and 1:3 which were prepared by deposition of Cu first had low activities towards ORR after dealloying. On the contrary, nanoparticles prepared by depositing Pt first exhibited promising electrocatalytic activities after dealloying. Samples with a Pt: Cu molar ratio of 1:3 showed higher activities than those with a molar ratio of 1:1. An enhanced ESA of 137 m(2)/g and dealloying induced enhanced mass activity of 0.123 A/mg(Pt) was obtained using the sample with a Pt: Cu molar ratio of 1:3, which was annealed at 800 degrees C. On the other hand, the same sample annealed at 950 degrees C had the highest specific activity of 0.165 mA/cm(2).

In this study, mass transfer limitations in a monolith reactor for selective catalytic reduction (SCR) of NOx were investigated. The reactor channels were washcoated with a commercial copper chabazite (CHA) catalyst. SCR experiments with different space velocities (20,000–80,000 h−1 (STP) range) were carried out. The feed to the reactor contained 300 ppm NH3, 300 ppm NO, 10% CO2, 8% O2, and 5% H2O with the balance being N2. NO conversion at steady state was measured between 100 and 590°C. Results revealed that the overall reaction rate is controlled by surface reactions up to 210°C but between 210 and 380°C both chemical reaction, internal and external mass transfer resistances are important. The maximum NO conversion was obtained for the highest flow rate above 350°C, therefore, external mass transfer rate dominates the overall reaction rate in this zone while the reactor operates in the kinetic regime at high flow rates and at low temperatures. Kinetic parameters for standard SCR reaction were determined using the data in the kinetically controlled region. Intrinsic rate constants were combined with the internal diffusion parameters to determine the apparent rate constants and the region where internal mass transfer limitations occur. Overall and apparent reaction rate parameters were used to extract the external mass transfer coefficients in the interphase diffusion controlled region. Various correlations for mass transfer coefficient for monolith reactors were compared with the external mass transfer coefficients found in this study.

Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me 2 ) is adsorbed from supercritical carbon dioxide (scCO 2 ) solutions onto Vulcan VX-72 at 13.2 MPa and 50 °C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N 2 at ambient pressure (route 1), thermal conversion in scCO 2 (route 2), or chemical conversion in H 2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes.

Supercritical deposition is an alternative technique to incorporate metals on supports. It has been used to deposit a wide variety of single or multi-metallic morphologies such as highly dispersed species, nanoparticles, nanorods and conformal films on high surface area supports, polymers and crystalline substrates. Preparation consists of three main stages which are the dissolution of a metal complex in a supercritical fluid, adsorption or sorption of the metal complex onto support and the conversion of the adsorbed complex to metal species. Studies associated with each of these stages were described along with a thorough summary of recent studies on the preparation of the aforementioned materials. Perspectives for future studies were presented at the end of each section.

Supercritical deposition was used to synthesize Pt/carbon aerogel (Pt/CA) electrocatalysts. CAs with average pore diameters of 6, 8 and 19 nm (CA6, CA8 and CA19, respectively) were synthesized and impregnated with Pt(cod)me(2) precursor using supercritical carbon dioxide followed by the thermal conversion of the Pt precursor into its metallic form under N-2 atmosphere at various temperatures between 200 and 1000 degrees C. All of the prepared CAs have high surface areas with very sharp pore size distributions. XRD and TEM results show increased Pt particle size with increasing conversion temperature with a homogenous distribution of nanoparticles on the CA supports. Cyclic voltammetry was used to determine the effect of CA pore properties on electrocatalytic activity. At a conversion temperature of 400 degrees C, the highest and lowest electrochemical surface area values were obtained for Pt/CA19 and Pt/CA6 of (126 and 36 m(2)/g, respectively). Furthermore, Pt/CA19 showed good mass activity whereas Pt/CA6 and Pt/CA8 had lower activity values towards the Oxygen Reduction Reaction (ORR). The mass activity values for Pt/CA19 increased with increasing conversion temperature, except for the sample converted at 1000 degrees C which exhibited the lowest mass activity. The specific activity increased significantly with the conversion temperature up to 600 degrees C which gave a value six times that obtained at 200 degrees C. At 800 degrees C, the specific activity decreased slightly, probably due to a change in the CA structure at this elevated conversion temperature. The Pt/CA19 sample converted at 600 degrees C exhibited the best performance with a mass activity of 0.1 A/mg(pt) and a specific activity of 0.24 mA/cm(2). (C) 2017 Elsevier Inc. All rights reserved.

Optofluidic components enable flexible routing and transformations of light beams in integrated lab-on-a-chip systems with the use of carefully shaped fluid parcels. For structural integrity reasons, the working fluid is typically contained within a solid-material chip. One of the outstanding challenges in optofluidics is the preparation and processing of optofluidic waveguides. These require solid cladding materials that are sufficiently strong to contain the fluid while possessing optical properties that allow efficient confinement of light within fluidic channels. Here, we report on a new technique to obtain liquid-core optofluidic waveguides based on total internal reflection of light in three-dimensional water-filled channels embedded in hydrophobic silica aerogel. To form the channels, we employ a fiber made of cage-like silicon-oxygen compound – trifluoropropyl polyhedral oligomeric silsesquioxane (trifluoropropyl POSS) – which has high solubility in supercritical CO 2 (scCO 2 ). A U-shaped fiber made of trifluoropropyl POSS is obtained by melt/freeze processing of POSS powder and subsequently placed in a silicate sol. After gelation of the sol and aging of the gel, scCO 2 extraction is used to dry the wet gel and extract the POSS fiber, yielding a dry silica aerogel with a U-shaped empty channel inside it. Finally, the silanol groups at the surface of the aerogel are reacted with hexamethyldisilazane (HMDS) in the presence of scCO 2 to render the aerogel surface hydrophobic and the channel is filled with water. We demonstrate efficient waveguiding by coupling light into the water-filled channel and monitoring the channel output. The presented procedure opens up new possibilities for creating complex three-dimensional networks of liquid channels in aerogels for optofluidic applications.

Carbon aerogel (CA)–nickel nanocomposites were synthesized by impregnating the CAs with nickel(II) acetylacetonate (Ni(acac) 2 ) from supercritical carbon dioxide at 30 MPa and 60 °C followed by thermal or chemical treatment using H 2 at atmospheric pressure. The CA–Ni(acac) 2 –CO 2 adsorption isotherm was measured at the impregnation condition and found to be linear. The decomposition of Ni(acac) 2 on the CA surface was investigated using thermo-gravimetry and mass-spectroscopy. Propane was found in the gaseous decomposition products. CA–Ni composites were characterized using Infrared (IR) Spectroscopy and characteristic Ni(acac) 2 peaks were found to disappear after thermal or chemical treatments. X-ray diffraction (XRD) data confirmed that after H 2 treatments nickel nanocrystals were present in the CA. Transmission electron microscopy (TEM) revealed the presence of nickel nanostructures dispersed homogeneously on the surface of the CA. In the samples treated with H 2 at 170 °C, the average Ni nanoparticle size increased from 4.9 to 12.9 nm when the Ni loading increased from 3 to 6.5 wt.%. The H 2 treatment at 200 °C resulted in Ni nanorods with diameters of 7–11 nm and lengths of 25–50 nm dispersed throughout the CA surface.

Fuel cells (FCs) are emerging as devices for electricity generation in a new economic era where energy is increasingly obtained from renewable sources. FCs operate with relatively higher efficiencies as compared to internal combustion engines due to the direct conversion of chemical energy to electricity by electrochemical reactions. However, there exist a number of obstacles for their widespread acceptance and integration in our daily lives. These obstacles can be summarized as the high cost of FCs due to the high costs of materials, the need to process fuels to very high-purity levels, the unacceptable declines in performance with time as well as the absence of a H2 infrastructure. Applications of supercritical fluids (SCFs) in synthesis of novel materials and development of new processing techniques offer a wide range of opportunities that can help commercialization of FCs. These include the preparation of micro or nanoarchitectured materials in a highly controllable manner for electrolyte-electrode assemblies of a wide variety of FCs including proton exchange membrane FCs (PEMFCs) and solid oxide FCs (SOFCs). In this extent, materials synthesized using SCFs are (at least) comparable or superior in performance as compared to their conventional counterparts. The synthesis and processing of novel materials necessary for efficient hydrogen storage/processing and design of novel processes for H2 production may also benefit from the use of SCFs.

Carbon aerogel (CA) supported Pt-Cu bimetallic nanoparticles were synthesized via simultaneous adsorption of bis(1,1,1,3,5,5,6,6,6-nonafluorohexane-2,4-diiminate)copper (CuDI6) and dimethyl(1,5-cyclooctadiene)platinum(II) (Pt-(cod)me(2)) onto CM in the presence of supercritical carbon dioxide (scCO(2)) and subsequent thermal conversion at ambient pressure. Binary adsorption isotherms of metal precursors on CM in scCO(2) were measured at 35 degrees C and 10.6 MPa by analyzing the fluid phase concentrations in a batch system and could be predicted from pure component adsorption isotherms using ideal adsorbed solution theory (IAST). Homogeneously dispersed Pt-Cu nanoparticles were formed on the surface of the CM via the thermal conversion of the precursors at 400 degrees C. As the Pt/Cu ratio decreased from 97:3 to 21:79, both the mean and the standard deviation of the particle size increased from 2.9 to 7.2 nm and from 1.3 to 3.7 nm, respectively. The alloying of Pt and Cu within the nanoparticles was confirmed via XRD peak shifts, and XPS data indicated that the surfaces of these Pt-Cu alloy nanoparticles were enriched in Pt.

A supercritical deposition method has been used to synthesize aerogel-copper nanocomposites. Carbon, resorcinol-formaldehyde, and silica aerogels (CAs, RFAs, and SAs) were impregnated with a new polyfluorinated copper precursor (CuDI6), which has a high solubility in supercritical carbon dioxide (scCO(2)). Adsorption isotherms of CuDI6 onto various aerogels from scCO(2) were determined at 35 degrees C and 10.6 MPa using a batch method which is based on the measurement of the fluid phase concentration. The relative affinity between CuDI6 and different aerogels changed in the following order: CA > RFA > SA. The effect of temperature on the adsorption isotherms for the CuDI6-CO2-CA system was also studied at 35 and 55 degrees C and at a CO2 density of 736.1 kg/m(3). The CuDI6 uptake at a particular CuDI6 concentration increased with increasing temperature. Adsorbed CuDI6 was found to convert into Cu and Cu/Cu2O nanoparticles on the aerogel supports after chemical or thermal treatments at ambient pressure and at temperatures ranging from 200 to 400 degrees C.

Nanostructured materials have been attracting increased attention for a wide variety of applications due to their superior properties compared to their bulk counterparts. Current methods to synthesize nanostructured materials have various drawbacks such as difficulties in control of the nanostructure and morphology, excessive use of solvents, abundant energy consumption, and costly purification steps. Supercritical fluids especially supercritical carbon dioxide (scCO(2)) is an attractive medium for the synthesis of nanostructured materials due to its favorable properties such as being abundant, inexpensive, non-flammable, non-toxic, and environmentally benign. Furthermore, the thermophysical properties of scCO(2) can be adjusted by changing the processing temperature and pressure. The synthesis of nanostructured materials in scCO(2) can be classified as physical and chemical transformations. In this article, Part I of our review series, synthesis of nanostructured materials using physical transformations is described where scCO(2) functions as a solvent, an anti-solvent or as a solute. The nanostructured materials, which can be synthesized by these techniques include nanoparticles, nanowires, nanofibers, foams, aerogels, and polymer nanocomposites. scCO(2) based processes can also be utilized in the intensification of the conventional processes by elimination of some of the costly purification or separation steps. The fundamental aspects of the processes, which would be beneficial for further development of the technologies, are also reviewed.