Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO₂

The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during the reaction were investigated. The photocatalytic WGSR rate under light excitation with wavelengths extending from 320 to 1100 nm was found to be higher than the thermal reaction alone at the same temperature (85 °C). A H2/CO2 ratio of near unity was found at high concentrations of CO. The addition of molecular oxygen during the reaction resulted in a slight decrease in molecular hydrogen production, while the rates of CO2 formation and CO consumption changed by one order of magnitude. More importantly, it was found that the WGSR rates were still high under only visible light excitation (600–700 nm). The results prove that Au LSP alone triggers this chemical reaction without requiring the excitation of the semiconductor on which they are deposited

Adsorption of hydrogen on the surface and sub-surface of Cu(111)

The interaction of atomic hydrogen with the Cu(111) surface was studied by a combined experimental-theoretical approach, using infrared reflection absorption spectroscopy, temperature programmed desorption, and density functional theory (DFT). Adsorption of atomic hydrogen at 160 K is characterized by an anti-absorption mode at 754 cm−1 and a broadband absorption in the IRRA spectra, related to adsorption of hydrogen on three-fold hollow surface sites and sub-surface sites, and the appearance of a sharp vibrational band at 1151 cm−1 at high coverage, which is also associated with hydrogen adsorption on the surface. Annealing the hydrogen covered surface up to 200 K results in the disappearance of this vibrational band. Thermal desorption is characterized by a single feature at ∼295 K, with the leading edge at ~250 K. The disappearance of the sharp Cu-H vibrational band suggests that with increasing temperature the surface hydrogen migrates to sub-surface sites prior to desorption from the surface. The presence of sub-surface hydrogen after annealing to 200 K is further demonstrated by using CO as a surface probe. Changes in the Cu-H vibration intensity are observed when cooling the adsorbed hydrogen at 180 K to 110 K, implying the migration of hydrogen. DFT calculations show that the most stable position for hydrogen adsorption on Cu(111) is on hollow surface sites, but that hydrogen can be trapped in the second sub-surface layer.Fil: Mudiyanselage, Kumudu. Brookhaven National Laboratory; Estados UnidosFil: Yang, Yixiong. State University Of New York; Estados UnidosFil: Hoffmann, Friedrich M.. City University Of New York; Estados UnidosFil: Furlong, Octavio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Física Aplicada; ArgentinaFil: Hrbek, Jan. Brookhaven National Laboratory; Estados UnidosFil: White, Michael G.. Brookhaven National Laboratory; Estados UnidosFil: Liu, Ping. Brookhaven National Laboratory; Estados UnidosFil: Stacchiola, Dario Jose. Brookhaven National Laboratory; Estados Unido

Hydrogenation and dehydrogenation of nitrogen containing species on the platinum(111) surface.

Hydrogenation and dehydrogenation of nitrogen containing species on the platinum(111) surface

Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO₂

The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during the reaction were investigated. The photocatalytic WGSR rate under light excitation with wavelengths extending from 320 to 1100 nm was found to be higher than the thermal reaction alone at the same temperature (85 °C). A H2/CO2 ratio of near unity was found at high concentrations of CO. The addition of molecular oxygen during the reaction resulted in a slight decrease in molecular hydrogen production, while the rates of CO2 formation and CO consumption changed by one order of magnitude. More importantly, it was found that the WGSR rates were still high under only visible light excitation (600–700 nm). The results prove that Au LSP alone triggers this chemical reaction without requiring the excitation of the semiconductor on which they are deposited

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

The structure-reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0 < theta(BaO) < 30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in the initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (< 4 ML), BaO clusters (< 1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)(2) forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)(2) phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)(2) phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)(2) are identical, i.e., both of these phases can completely be converted to Ba(NO3)(2). In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these "carbonated" BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(< 1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)(2) was also substantiated in experiments where Ba(NO3)(2)/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition.close

Potential use of mud clam (Geloina coaxans) in producing sauce with papaya crude extraction as a protein hydrolysing agent

Mud clam (Geloina coaxans) are underutilised food source due to the lack of consumer preference in Sri Lanka. Hence, this study was conducted to produce clam sauce as a value added product using the muscle of mud clams by means of accelerated fermentation method. Specimens were collected from Tambalagam Bay, Sri Lanka. Shell length, height, inflation, total weight with shell and without shell were 6.3 ± 0.4 cm, 5.3 ± 0.3 cm, 3.5 ± 0.3 cm, 83.1 ± 13.4 g and 14.9 ± 1.3 g respectively. The extracted mean meat yield was 14.9 ± 1.3% per mud clam. Moisture, crude protein, crude lipid and ash (dry weight) content of raw meat were 80.45 ± 0.89%, 64.14 ± 0.96%, 3.55 ± 0.39% and 7.54 ± 0.61% respectively. Final sauce product shows liquid yield, energy value, 0Brix value, pH, % NaCl, total nitrogen, moisture and ash content as 98.3 ± 5.5 ml 100g–1, 2124 ± 133 J g–1, 24.3 ± 0.9%, 5.02 ± 0.04, 14.53 ± 0.27%, 0.27 ± 0.01%, 74.06 ± 0.56% and 19.66 ± 1.99% respectively. The study concluded that the mud clam meat is a possible candidate as a raw material for the production of clam sauce

Effect of K loadings on nitrate formation/decomposition and on NOx storage performance of K-based NOx storage-reduction catalysts

We have investigated the effect of K loadings on the formation and the decomposition of KNO3 over K2O/Al2O3, and measured NOx storage performance of Pt-K2O/Al2O3 catalysts with various potassium loadings. After NO2 adsorption on K2O/Al2O3 at room temperature, ionic and bidentate nitrates were observed by Fourier transform infra-red (FTIR) spectroscopy. The ratio of the former to the latter species increased with increasing potassium loading up to 10wt%, and then stayed almost constant with additional K, demonstrating a clear dependence of loading on potassium nitrate formed. Although both K2O(10)/Al2O3 and K2O(20)/Al2O3 samples formed similar nitrate species identified by FTIR obtained after NO2 adsorption, the latter has more thermally stable nitrate species as evidenced by FTIR and NO2 temperature programmed desorption (TPD) results. With regard to NOx storage-reduction performance of Pt-K2O/Al2O3 samples, the temperature of maximum NOx uptake (Tmax) is 573K up to a potassium loading of 10wt%. As the potassium loading increases from 10wt% to 20wt%, Tmax shifted from 573K to 723K. Moreover, the amount of NO uptake (38cm3 NOx/gram of catalyst) at Tmax increased more than three times, indicating that efficiency of K in storing NOx is enhanced significantly at higher temperature, in good agreement with the NO2 TPD and FTIR results. Thus, a combination of characterization and NOx storage performance results demonstrates an unexpected effect of potassium loading on nitrate formation and decomposition processes; results important for developing Pt-K2O/Al2O3 as potential catalysts as high temperature NOx storage-reduction applications.close2