Vibrational Analysis of H₂ and D₂ Adsorption on Pt/SiO₂

Abstract

Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)3SiOSi(OH)3. The spectroscopy experiments showed reversible formation of isolated OH and OD groups on the silica surface when the samples were exposed to H2 and D2, respectively. In addition to the absorption peak corresponding to isolated OH and OD groups, an intense broad band was observed around 3270 cm(-1) (2500 cm(-1)) during H2 (D2) exposure. Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. The surface coverage of new OH groups was found to correlate to the platinum loading in the samples, indicating that the new silanol groups were formed in the vicinity of the Pt particles. In the investigated temperature interval, the formation rate of OH groups was not found to be temperature dependent.

Highly Selective Continuous Flow Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol in a Pt/SiO2 Coated Tube Reactor

“…The appearance of the peak centered at 460 • C indicates the formation of acid sites formed, likely at the vicinity of the Pt nanoparticles. The formation of new acidic groups on the Pt/SiO 2 catalysts agrees with the literature data, but strongly depends on the catalyst preparation method [45][46][47]. …”

Development of SiC-FET methanol sensor

“…On the other hand, the high concentration also introduced the interesting extremely high response of the Pt gate sensor, for which we can only speculate about the reason. It can be assumed that part of the response is due to hydrogen atoms decomposed from methanol, which are detected as OH groups formed on the insulator surface in the normal way for hydrogen containing gases by these sensors [22]. A theoretical value for the saturated hydrogen response for a thick film sensor is about 800 mV and for a porous film about 200 mV adds to the response from consumption of oxygen ions adsorbed on the insulator surface by the hydrogen [23,24].…”

Catalytic properties of oxide nanoparticles applied in gas sensors

“…There is evidence of these phenomena after investigation by DRIFT spectroscopy using model surfaces of Pt or Ir impregnated SiO 2 powder. Clear evidences for OH groups and even eventually OH 2 + groups were found on the SiO 2 sites during hydrogen and ammonia exposure in air [10,11].…”

“…Another interesting thing to note in the results in figure 5 is the response to the combination of NO/NH 3 , which seems to be simply the addition of the single responses indicating an independent detection mechanism for NH 3 and NO x , respectively. While the detection mechanism for NH 3 is quite well understood [10,11,13] the mechanism for detection of NO x is still under investigation. Finally it can be noticed that for the structure of the sample containing the indium oxide layer between two Au droplet deposited layers the reproducibility of the signal after a number of test cycles was very poor, indicating a kind of capacitor properties breakdown, for example related to a leakage current in the insulator of the device.…”