Pulse Surface Reaction Rate Analysis Research Articles

Design of Fischer-Tropsch catalysts by PSRA

For the design of the Fischer-Tropsch catalyst, the promoter to Ru/Al 2O 3 catalyst was selected on the basis of the working hypothesis that fast C–O bond dissociation and slow hydrogenation of surface carbon species would lead to high activity and selectivity for liquid fuel fraction. The rate constants of these surface reactions were measured by the PSRA (Pulse Surface reaction Rate Analysis) in the hydrogenation of CO on Ru/Al 2O 3 with several kinds of additives. Oxides of V, Nb, Mo, and W, which satisfied the working hypothesis, were selected as the promoter. The continuous flow reaction under pressure confirmed that these promoters resulted in higher activity and selectivity, indicating the effectiveness of the PSRA for the catalyst design.

Effect of alkaline additives on the C−O bond dissociation of adsorbed CO in methanation over Ru/Al2O3 catalyst

By using PSRA (Pulse Surface Reaction Rate Analysis) coupled with EDR (Emissionless Diffuse Reflectance Infrared Spectrometer), it was found that the lower shift of C−O stretching vibration of absorbed CO — caused by the addition of alkali carbonate to Ru/Al2O3 — leads to a decrease in the rate constant for the C−O dond dissociation process of adsorbed CO in methanation.

Electronic effects of alkaline carbonates in methanation over Pd/Al 2O 3 catalysts

Electronic effects of alkaline carbonates on the C-O bond dissociation of adsorbed CO in methanation over Pd/Al 2O 3 catalysts were investigated by using a pulse surface reaction rate analysis (PSRA) coupled with an emissionless diffuse reflectance infrared spectroscopy (EDR). Alkaline carbonates added to the Pd/Al 2O 3 catalyst exist mainly on the alumina support. This addition causes the IR bands of adsorbed CO to shift to lower frequencies, and markedly decreases the rate constant for the C-O bond dissociation. It was concluded that the addition of alkaline carbonates to the Pd/Al 2O 3 catalyst increases the electron density of the Pd metal which in turn decreases the rate constant for the C-O bond dissociation of adsorbed CO. This relationship was explained in terms of a partially hydrogenated CO species which acts as intermediate for the C-O bond dissociation of adsorbed CO in methanation.

Promoting effect of V, Mo, W, and Re on the rate of C–O bond dissociation of adsorbed CO in methanation on Ru/Al2O3

Using pulse surface reaction rate analysis coupled with an emissionless diffuse reflectance infrared spectrometer, it has been found that addition of V, Mo, W, or Re greatly increases the rate of C–O bond dissociation of adsorbed CO in methanation on Ru/Al2O3.

Surface reaction rate of hydrogenation of adsorbed carbon monoxide as examined by an emissionless infrared diffuse reflectance spectrometer

The behaviors of adsorbed CO species during the methanation of CO on supported metal catalysts were examined by using an EDR (emissionless infrared diffuse reflectance spectrometer). Major adsorbed species observed under steady-state CO-H/sub 2/ reaction were adsorbed CO and surface formate, and appreciable absorption could not be observed in C-H and O-H regions. The rate constants of disappearance of adsorbed species on 0.5% Pd/Al/sub 2/O/sub 3/ under the reaction conditions were also measured from the transient responses of IR spectra. The intensities of the bands due to surface formate did not change with time, showing that the surface formate is not an intermediate. The rate constants of disappearance of adsorbed CO (linear CO and bridge CO) were essentially identical with each other and were in good agreement with the rate constant of CH/sub 4/ formation measured by PSRA (pulse surface reaction rate analysis). These data indicate that the rate-determining step in the methanation of CO is the C-O bond dissociation of adsorbed species and the hydrogenation of the adsorbed carbon species proceeds rapidly. 8 figures, 1 table.

Kinetics, isotope effects, and mechanism of the hydrogenation of carbon monoxide on a supported palladium catalyst

Kinetics and isotope effects for the C-O bond dissociation in the hydrogenation of CO on palladium/alumina (Pd/Al/sub 2/O/sub 3/) catalyst were investigated by using pulse surface reaction rate analysis (PSRA). The rate-determining step was found to be the C-O bond dissociation of the adsorbed CO species. The rate constant for the C-O bond dissociation process per adsorbed CO molecule was determined at various temperatures and Arrhenius parameters of the rate constant were obtained. The rate constant in flowing deuterium (D/sub 2/)(k/sub D/) was considerably larger than that in flowing H/sub 2/(k/sub H/), indicating an inverse isotope effect. The average value of k/sub H//k/sub D/ was 0.61. The extent of the inverse isotope effect for Pd was more significant than that for nickel (Ni)(k/sub H//k/sub D/ = 0.75). The preexponential factor for k/sub H/ on Pd (1.6 x 10/sup 4/s/sup -1/) was much smaller than that on Ni (5.4 x 10/sup 6/s/sup -1/). It was concluded that adsorbed CO is not directly dissociated to surface carbon and oxygen atoms but hydrogen atoms play an important role in the C-O bond dissociation. Further details of the mechanism for the C-O bond dissociation were discussed from the observed kinetics and isotope effects. 5more » figures.« less

ChemInform Abstract: KINETICS, ISOTOPE EFFECTS, AND MECHANISM FOR THE HYDROGENATION OF CARBON MONOXIDE ON SUPPORTED NICKEL CATALYSTS

Kinetics and hydrogen-deuterium isotope effects in the methanation of adsorbed CO molecules on a Ni/SiO/sub 2/ catalyst were precisely measured by using pulse surface reaction rate analysis (PSRA). When a CO pulse was injected into flowing hydrogen, it was immediately adsorbed on the catalyst and gradually hydrogenated to CH/sub 4/ and H/sub 2/O. The amounts of CH/sub 4/ and H/sub 2/O produced by the hydrogenation of the adsorbed CO were determined up to various times, and it was found that CH/sub 4/ and H/sub 2/O were produced at the same rate. When O/sub 2/ instead of CO was injected, H/sub 2/O was immediately produced. From these results, the rate-determining step of the reaction was found to be C-O bond dissociation of an adsorbed CO molecule or a partially hydrogenated CO species. By PSRA, the rate constant for the C-O bond dissocition process per adsorbed CO molecule (k/sub H/) was determined at various temperatures, and the Arrhenius parameters of the rate constant were obtained. The rate constant in flowing deuterium (k/sub D/) was also determined. it was found that k/sub D/ is considerably larger than k/sub H/, indicating an inverse isotope effect. The average value of k/sub H//k/sub D/ was 0.75.more » From these results, it was concluded that adsorbed CO is not directly dissociated to surface carbon and oxygen atoms but it is partially hydrogenated before C-O bond dissociation under the conditions of the PSRA experiment. 8 figures.« less

Kinetics, isotope effects, and mechanism for the hydrogenation of carbon monoxide on supported nickel catalysts

Kinetics and hydrogen-deuterium isotope effects in the methanation of adsorbed CO molecules on a Ni/SiO/sub 2/ catalyst were precisely measured by using pulse surface reaction rate analysis (PSRA). When a CO pulse was injected into flowing hydrogen, it was immediately adsorbed on the catalyst and gradually hydrogenated to CH/sub 4/ and H/sub 2/O. The amounts of CH/sub 4/ and H/sub 2/O produced by the hydrogenation of the adsorbed CO were determined up to various times, and it was found that CH/sub 4/ and H/sub 2/O were produced at the same rate. When O/sub 2/ instead of CO was injected, H/sub 2/O was immediately produced. From these results, the rate-determining step of the reaction was found to be C-O bond dissociation of an adsorbed CO molecule or a partially hydrogenated CO species. By PSRA, the rate constant for the C-O bond dissocition process per adsorbed CO molecule (k/sub H/) was determined at various temperatures, and the Arrhenius parameters of the rate constant were obtained. The rate constant in flowing deuterium (k/sub D/) was also determined. it was found that k/sub D/ is considerably larger than k/sub H/, indicating an inverse isotope effect. The average value of k/sub H//k/sub D/ was 0.75.more » From these results, it was concluded that adsorbed CO is not directly dissociated to surface carbon and oxygen atoms but it is partially hydrogenated before C-O bond dissociation under the conditions of the PSRA experiment. 8 figures.« less