Water–gas shift activity of pt catalysts prepared by different methods

Platinum supported on ceria and zirconia was prepared through different preparation methods: Coprecipitation (CP), spray drying (SD), and flame spray pyrolysis (FSP). The catalysts were characterized by XRD, TPR, N2 adsorption, and H2 chemisorption, and the water–gas shift activity in the range 190–310 ◦C and initial stability at 300–310 ◦C were tested. Although the spray-dried Pt/CeO2/ZrO2 catalyst shows the highest initial activity, it deactivates rapidly at 300 ◦C and levels out at similar activity as the coprecipitated Pt/CeO2 and Pt/CeO2/ZrO2 within a few hours. Flame spray pyrolysis appears to be a promising preparation method concerning the stability of catalysts, although the initial activity is rather poor. High activity is related to high Pt dispersion, low reduction temperature, and small support particles. The support particle size is also much affected by the preparation method

Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd3Au(100)

The CO oxidation behavior under excess oxygen and near stoichiometric conditions over the surface of Pd3Au(100) has been studied by combining near-ambient pressure X-ray photoelectron spectroscopy and quadrupole mass spectrometry and compared to Pd(100). During heating and cooling cycles, normal hysteresis in the CO2 production, i.e. with the light-off temperature being higher than the extinction temperature, is observed for both surfaces. On both Pd3Au(100) and Pd(100) the (√5 × √5)R27° surface oxide structure is present during CO2 production under excess oxygen conditions (O2:CO = 10:1), while at near stoichiometric conditions (O2:CO = 1:1) the surfaces are covered with atomic oxygen. Au as alloying element hence induces only minor differences in the observed hysteresis and the active phase compared to pure Pd. Alloying with Au thus yields a different behavior compared to Ag, where reversed hysteresis is observed for CO2 production over Pd75Ag25(100) at similar conditions [Fernandes et al., ACS Catal. (2016) 4154]

Interaction of hydrogen with flat (0001) and corrugated (11–20) and (10–12) cobalt surfaces: insights from experiment and theory

Cobalt catalysts are used on a commercial scale to produce synthetic fuels via the Fischer-Tropsch synthesis process. As adsorbed hydrogen atoms are involved in many of the elementary reaction steps that occur on the catalyst surface during the reaction it is of interest to study how the structure of the catalyst surface affects the reactivity with di-hydrogen as well as with adsorbed hydrogen atoms. In the present study we use a combination of experimental and theoretical methods to gain insight into how the structure of a cobalt surface affects the H 2 dissociation reaction and the adsorption bond strength of the hydrogen atoms produced in this step. A comparison of the open Co(11–20) and (10–12) surfaces with the flat, close packed Co(0001) surface confirms that undercoordinated Co atoms strongly enhance the rate of H 2 dissociation. At the same time, the lower desorption temperatures found on the more open surfaces indicate that the bond strength of adsorbed hydrogen decreases, in the following order: Co(0001)>Co(10–12)>Co(11–20). DFT calculations confirm this trend, showing that hydrogen adsorbs weaker on the more open surfaces for both low and high coverages. In the context of the Fischer-Tropsch synthesis reaction we propose that step and kink sites are important for efficient H 2 dissociation. After dissociation, the higher hydrogen adsorption strength on terrace sites would promote diffusion away from the dissociation site to flat terraces where they can participate in hydrogenation reactions

Deactivation of Co-Based Fischer–Tropsch Catalyst by Aerosol Deposition of Potassium Salts

A 20%Co/0.5%Re/γAl₂O₃ Fischer–Tropsch catalyst was poisoned by four potassium salts (KNO₃, K₂SO₄, KCl, and K₂CO₃) using the aerosol deposition technique, depositing up to 3500 ppm K as solid particles. Standard characterization techniques (H₂ chemisorption, BET, TPR) showed no difference between treated samples and their unpoisoned counterpart. The Fischer–Tropsch activity was investigated at industrially relevant conditions (210 °C, H₂:CO = 2:1, 20 bar). The catalytic activity was significantly reduced for samples exposed to potassium, and the loss of activity was more severe with higher potassium loadings, regardless of the potassium salt used. A possible dual deactivation effect by potassium and the counterion (chloride and sulfate) is observed with the samples poisoned by KCl and K₂SO₄. The selectivity toward heavier hydrocarbons (C₅₊) was slightly increased with increasing potassium loading, while the CH₄ selectivity was reduced for all the treated samples. The results support the idea that potassium is mobile under FT conditions. The loss of activity was described by simple deactivation models

Interaction of hydrogen with flat (0001) and corrugated (11–20) and (10–12) cobalt surfaces:insights from experiment and theory

\u3cp\u3e Cobalt catalysts are used on a commercial scale to produce synthetic fuels via the Fischer-Tropsch synthesis process. As adsorbed hydrogen atoms are involved in many of the elementary reaction steps that occur on the catalyst surface during the reaction it is of interest to study how the structure of the catalyst surface affects the reactivity with di-hydrogen as well as with adsorbed hydrogen atoms. In the present study we use a combination of experimental and theoretical methods to gain insight into how the structure of a cobalt surface affects the H \u3csub\u3e2\u3c/sub\u3e dissociation reaction and the adsorption bond strength of the hydrogen atoms produced in this step. A comparison of the open Co(11–20) and (10–12) surfaces with the flat, close packed Co(0001) surface confirms that undercoordinated Co atoms strongly enhance the rate of H \u3csub\u3e2\u3c/sub\u3e dissociation. At the same time, the lower desorption temperatures found on the more open surfaces indicate that the bond strength of adsorbed hydrogen decreases, in the following order: Co(0001)>Co(10–12)>Co(11–20). DFT calculations confirm this trend, showing that hydrogen adsorbs weaker on the more open surfaces for both low and high coverages. In the context of the Fischer-Tropsch synthesis reaction we propose that step and kink sites are important for efficient H \u3csub\u3e2\u3c/sub\u3e dissociation. After dissociation, the higher hydrogen adsorption strength on terrace sites would promote diffusion away from the dissociation site to flat terraces where they can participate in hydrogenation reactions. \u3c/p\u3