Chemisorption and Catalysis over TiO<sub>2</sub>-Modified Pt Surfaces

Dwyer, Daniel J.; Robbins, John L.; Cameron, S. D.; Dudash, N.; Hardenbergh, J. H.

doi:10.1021/bk-1986-0298.ch003

Cited by 11 publications

(7 citation statements)

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“…Further, the fact that the number of reduced Ti cations is the same regardless of reduction temperature between 573 and 773 K is exactly consistent with the overlap of these reduction profiles at long reduction times. Our results are also consistent with those reported for several other titania-supported group VIII metal catalysts. ,,− …”

Section: Discussionsupporting

confidence: 93%

“…Our results are also consistent with those reported for several other titania-supported group VIII metal catalysts. 17,35,[57][58][59][60][61] The discontinuity in the Arrhenius plot observed in Figure 7 has been suggested in the previous analysis to result from a change in the rate-determining step. Under the simple reaction scheme chosen for its ability to explain the observed kinetics data, only one step (step 2) can be rate limiting at low temperatures and provide a satisfactory explanation of the kinetics.…”

Section: Discussionmentioning

confidence: 97%

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Isothermal Reduction Kinetics of Titanium Dioxide-Based Materials

Rekoske

Barteau

1997

J. Phys. Chem. B

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As metal oxide reduction may be a limiting or otherwise important step in a reaction cycle, a complete description of the kinetics of the reduction can be critical to the successful choice of catalytic material. Unfortunately, such information is often lacking. Such is the case in our attempts to develop a catalytic cycle from the stoichiometric reductive carbonyl coupling reaction on reduced TiO2 surfaces. To provide the necessary reduction kinetics, reaction of the anatase and rutile forms of TiO2 with H2 has been studied from 573 to 773 K. A novel flow-through microreactor which provides time-resolved catalyst mass measurements to ±1 μg while maintaining a conventional, tubular reactor, gas−solid contacting pattern has been employed. A shift in the kinetic order with respect to H2 with increasing temperature occurs, from one-half order at 573 K to zero order at 673 K and above. A discontinuity was also observed within this same temperature range in Arrhenius plots of the reduction rates of both anatase and rutile TiO2; apparent activation energies determined were approximately 12 kcal mol-1 above and 29 kcal mol-1 below 623 K. Modification of the surface of anatase TiO2 with a sufficient loading of group VIII metals removes the Arrhenius plot discontinuity, increasing the rate of reduction and decreasing the apparent activation energy at low temperatures. A change in rate-determining step is indicated by these observations, and a mechanistic scheme which combines the current and previous observations within a single framework is proposed.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionmentioning

confidence: 97%

Isothermal Reduction Kinetics of Titanium Dioxide-Based Materials

Rekoske

Barteau

1997

J. Phys. Chem. B

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“…17 For encapsulated Pt supported on a TiO2 thin film, Dwyer et al observed significantly increased CO desorption from Pt in TPD experiments after annealing in ~7.5x10 -7 Torr O2 at 875 K for less than 1h. 19 Contrary to those studies, Pesty et al found no evidence for a de-encapsulation on a reduced Pt/TiO2(110) catalyst upon annealing in 1x10 -6 Torr O2 at up to 1000 K for 10 min in low energy ion scattering experiments, but proposed the formation of a new stoichiometric TiO2 layer on Pt particles. 7 Naitabdi et al observed a considerable encapsulation of Pt on a TiO2(110) support in 0.75 Torr O2 at 440 K 22 and the TiOx overlayer was described to grow significantly upon the exposure of O2 (here at ~ 750 Torr) at elevated temperature (600 °C) in a recent investigation.…”

Section: Introductionmentioning

confidence: 89%

“…by the addition of stabilizing compounds 15 or sputtering of the surface after its exposure to high temperatures. 16 While some authors claim that the encapsulation can also be reversed by O2 annealing 6,17,[18][19][20] , others report an oxidation of the particles and/or thickening of the titania encapsulation layer under such conditions. 7,[21][22][23] In their pioneering work on SMSI, Tauster et al reported that the change in chemisorption behavior of a reduced Pd/TiO2 powder catalyst upon O2 annealing at 773 K is completely reversible.…”

Section: Introductionmentioning

confidence: 99%

Tuning Strong Metal–Support Interaction Kinetics on Pt-Loaded TiO₂(110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study

Petzoldt¹,

Eder²,

Mackewicz³

et al. 2022

J. Phys. Chem. C

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Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal-support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the 'pressure gap' between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O2 and H2 on the SMSI-state of well-defined Pt/TiO2(110) catalysts at pressures of up to 0.1 Torr. By tuning the O2 pressure, we can either selectively oxidize the TiO2 support or both the support and the Pt particles.Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1x10 -5 Torr O2, but orders of magnitudes less effective at higher O2 pressures, where Pt is in an oxidic state.While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.

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“…Modelling of the CO suppression by TiO, decoration suggests that the concentration of nucleation sites for TiO, island growth is 4.5 x 1013 cm-2. Dwyer et aZ., 22 on the other hand, have reported that X.P.S. observations show a substantial concentration of Ti3+ for Ti0,-promoted Pt-black.…”

mentioning

confidence: 98%