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An improved single crystal adsorption calorimeter for determining gas adsorption and reaction energies on complex model catalysts
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Image of FIG. 1.
FIG. 1.

Schematic diagram showing the working principle of a single crystal adsorption calorimeter.

Image of FIG. 2.
FIG. 2.

Schematic overview of the experimental setup. The labeled components are (1) preparation chamber, (2) adsorption/reaction chamber, (3) gate valve, (4) magnetic transfer rod, (5) microcalorimeter, (6) ion gun, (7) optics for LEED and AES, (8) gas doser, (9) and (10) two metal evaporators, (11) QCM, (12) port for pyrometer, and (13) mass spectrometer.

Image of FIG. 3.
FIG. 3.

Schematic overview over the setup for reflectivity measurements. The labeled components are (1) He–Ne laser, (2) chamber window, (3) sample, (4) main photodiode, (5) sampler photodiode, (6) beamsplitter, and (7) polarizer.

Image of FIG. 4.
FIG. 4.

Overview of the main components in the adsorption/reaction chamber. The labeled components are (1) molecular beam source, (2) rotatable platform, (3) microcalorimeter, (4) in situ photodiode, (5) beam monitor, (6) sample holder mounting, (7) detector head of the microcalorimeter, (8) Cu platform carrying the sample holder mounting and the detector, (9) outer molecular beam aperture, (10) Allen wrench mounted on wobble stick, (11) translation screw, (12) vibration damping stack, (13) QMS, and (14) two gas dosers.

Image of FIG. 5.
FIG. 5.

Components of the microcalorimeter: (1) pyroelectric ribbon, (2) detector housing, (3) Cu platform carrying the detector housing and the sample holder mounting, (4) translation screw, (5) sample holder mounting, (6) conical head of the detector housing, (7) back view of the sample holder, (8) thermal reservoir, (9) Cu block, (10) copper wires, (11) sapphire plates, (12) vibration damping stack, (13) support columns, and (14) set screws.

Image of FIG. 6.
FIG. 6.

Molecular beam source: (1) glass capillary array, (2) inner pumping state, (3) gas inlet, (4) flexible bellow, (5) positions of translator screws (the screws are not shown), (6) outer beam aperture, (7) outer pumping stage, (8) nozzle aperture, (9) chopper, and (10) prism.

Image of FIG. 7.
FIG. 7.

Scheme of the laser calibration system. The labeled components are: (1) lens system, (2) wheel carrying the neutral density filters, (3) chamber window, (4) prism, and (5) chopper.

Image of FIG. 8.
FIG. 8.

(a) The calorimetric response to a train of laser pulses of different intensities onto a 1 μm thick Pt(111) sample at 300 K. (b) Peak-to-peak output voltage vs absorbed heat input to the sample showing the linearity of the detector response.

Image of FIG. 9.
FIG. 9.

(a) Intensity of the effusive beam source plotted as a function of the backing pressure. (b) Beam profile at the sample position obtained at the backing pressure 3.75 × 10−2 mbar.

Image of FIG. 10.
FIG. 10.

The calibration curve showing the dependence of the reflectivity of the calibration mirrors on the photodiode intensity ratio Imain/Isampler measured with He–Ne laser at 632.8 nm (black squares, see the explanation in the text). The positions of the reflectivities for different samples are indicated with the open circles.

Image of FIG. 11.
FIG. 11.

Comparison of the detector response curves for the energy input upon adsorption of CO molecules (a) and absorption of the laser light (b) on 1 μm thick Pt(111) sample at 300 K, (c) difference between the normalized detector responses shown in (a) and (b), proving negligible line shape difference.

Image of FIG. 12.
FIG. 12.

A typical dataset obtained upon adsorption of CO on 1 μm Pt(111) at 300 K (CO flux: 2.6 × 1013 CO molecules cm−2 per pulse or 0.017 ML/pulse). (a) The detector response from a train of CO pulses, (b) the energy released per CO pulse plotted as a function of pulse number, (c) time evolution of the QMS signal at amu 28 used for calculated the sticking probability, and (d) the sticking probability plotted as a function of pulse number.

Image of FIG. 13.
FIG. 13.

Sticking probability and adsorption heat of CO on Pt(111) at 300 K plotted as a function of CO surface coverage.

Image of FIG. 14.
FIG. 14.

CO sticking probability (a) and adsorption heat (b) on Pt(111) at 130 K plotted as a function of CO surface coverage.


Generic image for table
Table I.

Measurements contributing to the overall accuracy and precision of the microcalorimetric experiment.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An improved single crystal adsorption calorimeter for determining gas adsorption and reaction energies on complex model catalysts