Reaction kinetics studies were conducted for the conversions of ethanol and acetic acid over silica-supported Pt and Pt/Sn catalysts at temperatures from 500 to 600 K. Addition of Sn to Pt catalysts inhibits the decomposition of ethanol to CO, CH 4 , and C 2 H 6 , such that PtSn-based catalysts are active for dehydrogenation of ethanol to acetaldehyde. Furthermore, PtSn-based catalysts are selective for the conversion of acetic acid to ethanol, acetaldehyde, and ethyl acetate, whereas Pt catalysts lead mainly to decomposition products such as CH 4 and CO. These results are interpreted using density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) and Pt 3 Sn(111) surfaces. The Pt 3 Sn alloy slab was selected for DFT studies because results from in situ 119 Sn Mössbauer spectroscopy and CO adsorption microcalorimetry of silica-supported Pt/Sn catalysts indicate that Pt-Sn alloy is the major phase present. Accordingly, results from DFT calculations show that transition-state energies for C-O and C-C bond cleavage in ethanolderived species increase by 25-60 kJ/mol on Pt 3 Sn(111) compared to Pt(111), whereas energies of transition states for dehydrogenation reactions increase by only 5-10 kJ/mol. Results from DFT calculations show that transition-state energies for CH 3 CO-OH bond cleavage increase by only 12 kJ/mol on Pt 3 Sn(111) compared to Pt(111). The suppression of C-C bond cleavage in ethanol and acetic acid upon addition of Sn to Pt is also confirmed by microcalorimetric and infrared spectroscopic measurements at 300 K of the interactions of ethanol and acetic acid with Pt and PtSn on a silica support that had been silylated to remove silanol groups.

Less than 10% of the plastics generated globally are recycled, while the rest are incinerated, accumulated in landfills, or leach into the environment. New technologies are emerging to chemically recycle...

An exciting discovery in the area of heterogeneous catalysis is the observation that nanoparticles of gold on high-surfacearea supports exhibit high activity for oxidation of CO with O 2 (CO + 1/2 O 2 !CO 2 ) at room temperature. [1,2] This discovery is of particular relevance for the production of fuel-cell-grade hydrogen, since carbon monoxide must be removed from hydrogen streams generated by catalytic reforming of hydrocarbons.[3] The origins for the unique catalytic properties of supported gold catalysts are still unresolved. These properties have been related to changes in the electronic properties, the presence of defect sites, and the existence of strain for metallic gold nanoparticles. [4][5][6][7][8] Unique catalytic properties have also been related to the presence of sites associated with the catalyst support, such as cationic gold species, and sites at gold-support interfaces. [9,10] Here we show that it is possible to study the catalytic properties of metallic gold, without interference from a catalyst support, by using nanotubes of gold in polycarbonate membranes. These nanotubes exhibit catalytic activity for the oxidation of carbon monoxide by O 2 at room temperature, and this activity is enhanced by liquid water, promoted by increasing the pH of the solution, and increased using H 2 O 2 as the oxidizing agent. The rate can also be increased by depositing KOH within these nanotubes. These rates are comparable with those found in heterogeneous catalysis studies with gold nanoparticles on oxide supports, which suggests that the high activity of these latter catalysts may be related to the promotional effect of hydroxyl groups.Gold nanotubes of uniform size were prepared via a template-synthesis method by electroless deposition of gold [11] within the pores of a 10-mm-thick, track-etched polycarbonate membrane containing 220-nm-diameter pores.[12] All surfaces of the template membrane were first sensitized with a Sn II salt, activated by formation of a metallic Ag layer, followed by electroless deposition of gold for a period of 2 h. The gold nanotubes were cleaned with a 25 % HNO 3 solution for 15 h.[13] Hydrophobic or hydrophilic selfassembled monolayers were formed on gold nanotubes by rinsing the samples in ethanol for 20 min, followed by immersion for 17 h in solutions of ethanol containing HS(CH 2 ) 15 CH 3 or HS(CH 2 ) 15 COOH, respectively. [14] Gold nanotubes embedded within the pores of the polycarbonate template membranes were exposed by reactive ion etching (RIE) using an oxygen plasma to selectively etch approximately 2.3 mm of polycarbonate, leaving the gold nanotubes intact.[15] Figure 1 shows images from field-emission scanning electron microscopy (SEM) of the top surface of a template membrane after electroless deposition of gold followed by RIE. The images in Figure 1 reveal a high level of surface roughness; the length scale is % 53 nm. The membrane reactor used to study CO oxidation over gold nanotubes is shown schematically in Figure 2.[12] Table 1 shows results for the rate of...

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The effect of Sn addition to Pt/CeO 2 -Al 2 O 3 and Pt/Al 2 O 3 catalysts was studied with X-ray photoelectron spectroscopy (XPS), 119 Sn Mössbauer spectroscopy and adsorption microcalorimetry of CO at room temperature. Catalysts were reduced in situ at 473 ("non-SMSI state") and 773 K ("SMSI state"). 119 Sn Mössbauer and XPS results indicated that the presence of cerium in bimetallic catalysts inhibited reduction of tin.Furthermore, it was found that tin facilitated reduction of cerium (IV) to cerium (III).Microcalorimetric analysis indicated that cerium addition caused the appearance of a more heterogeneous distribution of active sites, whereas tin addition led to a higher homogeneity of these sites.

Reaction kinetics data were collected for isobutane conversion over a series of ultra stable Y (USY) zeolite catalysts with and without rare earth cations and subjected to various extents of dealumination by steaming. We conducted these reaction studies at low temperatures (523-573 K) using isobutane feed streams containing known levels of isobutylene (100-400 ppm) so that the kinetics were controlled by bimolecular hydride transfer and oligomerization/beta-scission processes with little or no participation of monomolecular initiation reactions. These experimental conditions led to stable catalyst performance with the main products of isobutane conversion being propane, n-butane, and isopentane, with smaller amounts of propylene, trans-2-butene, and cis-2-butene. The rates of formation of these products per Brønsted acid site (as counted by pyridine adsorption) depended exponentially on Brønsted acid site density, regardless of whether the catalyst contained rare earth cations. Kinetic modeling showed an exponential dependence of hydride transfer and oligomerization/ beta-scission reaction rates on Brønsted acid site density which translated into composite activation energies for these reactions having a linear relationship with site density. Based on results in the literature from theoretical calculations, we suggest that increasing Brønsted acid site density in zeolite Y leads to larger zeolite elasticity, increased stabilization of cationic transition states, and lower composite activation barriers for hydride transfer and beta-scission steps. The role of rare earth cations, therefore, is to ensure the retention of high Brønsted acid site density under hydrothermal conditions, such as in fluid catalytic cracking (FCC) regenerators, where steam would dealuminate the Y zeolite framework and reduce this site density. It is for this reason that hydride transfer reaction rates are high in the presence of rare earth cations and lead to higher yields of less olefinic gasoline during FCC.