To inhibit sintering of ∼5 nm supported Ni particles during dry reforming of methane (DRM), catalysts were stabilized with porous alumina grown by ABC alucone molecular layer deposition (MLD). The uncoated catalyst continuously deactivated during DRM at 973 K. In contrast, the DRM rates for the MLD-coated catalysts initially increased before stabilizing, consistent with an increase in the exposed nickel surface area with exposure to high temperatures. Post-reaction particles were smaller for the MLD-coated catalysts. Catalysts with only 5 MLD layers had higher DRM rates than the uncoated catalyst, and a sample with 10 MLD layers remained stable for 108 h.
Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1 to 2.4 nm.The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperatureprogrammed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH 4 dissociation energies).
Platinum nanoparticles were grown on alumina by atomic layer deposition using either H 2 or O 2 as the second half-reaction precursor. Particle diameters could be tuned between ∼1 and 2 nm by varying between use of H 2 and O 2 and by changing the number of ALD cycles. The use of H 2 as the second precursor led to smaller Pt particle sizes. Differences in particle size were found to be related to the availability of surface hydroxyl groups, which were monitored via in situ infrared spectroscopy during Pt ALD. Temperature-programmed desorption (TPD) of CO and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for adsorbed CO were used to characterize sites and coordination numbers of the nanoparticles. As expected, smaller nanoparticles had sites with lower average coordination numbers. The catalysts were evaluated for oxidative dehydrogenation of propane to propylene. Catalysts having the smallest Pt particles with the lowest coordination number (synthesized by one cycle of Pt ALD with H 2 ) had a C 3 H 6 selectivity of 37% at 14% conversion, whereas under the same reaction conditions the selectivity was less than 1% for larger (3.6 nm) commercial Pt catalysts at 9% conversion.
Investigation of the dissolution of cellulose in Ethylene Diamine (EDA)/Potassium thiocyanate (KSCN) solutions by infrared spectroscopy (FTIR) and thermal analysis (DSC) indicated that changes to the solvent during freeze thaw cycling of mixtures was consistent with increased interaction between cellulose and solvent. Thermal transitions in the system, however, occurred at temperatures outside the range used in thermal cycling to promote dissolution. Further exploration of the dissolution and mixing process indicated that mixing was the limiting step in solution formation. The dissolution of two types of cellulose with different molecular weights (Degree of Polymerization (DP)=210 and >1000) was studied using EDA/ KSCN solution as the solvent. The solubility and the dissolution rate of cellulose depended on both the solvent composition and cellulose molecular weight. Cellulose could dissolve faster in the solvent with lower salt concentration but the highest cellulose concentration was obtained in the solvent with 30$35% KSCN. Rheological measurements showed that cellulose solutions exhibited viscous solution behavior at low KSCN concentration but primarily elastic behavior at high salt concentration.
Polyethylene oxide (PEO) nanofibers containing discrete magnetic domains have been produced using both parallel plate and syringe-plate electrospinning configurations. Magnetite nanoparticles from a commercial ferrofluid (MSG W11, Ferrotech Corporation) were suspended in 1–2 wt% PEO-in-water solutions and electrospun to produce fibers with diameters as small as 150 nm. Transmission electron microscopy was used to study particle agglomeration in the resulting nanofibers as a function of particle loading and electrospinning conditions. Magnetic measurements using a SQUID magnetometer were used to characterize the DC and AC magnetic response of the fibers. Applications to anti-counterfeiting in the textile industry are discussed.
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