Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104)National Science Foundation (Grant DMR78-24185

Kappes, Manfred M.

Kinney, John B.

Staley, Ralph H.

Contains reports on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant DMR-78-24185

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VI. INTERFACIAL CHEMISTRYAcademic Research StaffProf. R.H. StaleyGraduate StudentsR.W. Jones J.B. KinneyM.M. Kappes J.S. UppalI. PHOTOACOUSTIC SPECTROSCOPY AND CHEMICALLY MODIFIED SURFACESJoint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant DMR-78-24185)Ralph H. Staley, Manfred M. Kappes, John B. KinneyWork has focused on using photoacoustic spectroscopy (PAS) to characterizethe results of chemical attachment reactions of molecules to surfaces and to studyheterogeneous catalyst systems and their reactions. Electronic spectra in theUV-visible and overtone bands in the near-IR have been utilized in these studies.We have also recently begun using photoacoustic detection with a Nicolet 7199 FTIRsystem to obtain spectra in the mid-infrared range. All samples were run using acell built in our laboratories that allows control of the gas composition in con-tact with the sample. The sample chamber can be sealed and detached, so that sam-ples can be loaded in a dry box. Temperature control of the sample stage is alsopossible.Ferrocene-centered reagents can be bound to the surface of high-surface-area(400 m2/g) silica powders by reaction of the silica with solutions of (1,1'-fer-rocenediyl) dimethylsilane (DMP), or related reagents. PAS reveals a band-positionshift from the unreacted reagent to the reacted product indicating ring opening ofthe strained C-Si-C linkage bridging the two cyclopentadienyl rings to yield asimple, monosubstituted ferrocene center attached to the surface. Reversible oxida-tion of the surface-bound ferrocene centers to ferricenium centers by washing withacidic solutions of benzoquinone is confirmed by photoacoustic spectra. The surface-confined ferricenium can be used to oxidize N,N,N',N'-tetramethyl-p-phenylenediaminePR No. 122(VI. INTERFACIAL CHEMISTRY)(TMPD) to TMPD. in solution; this reaction allows an estimate of the surface cover-age. This, in turn, provides a means to calibrate PAS signal response to surfacefor the powder used.Similar use of PAS has been employed to monitor attachment chemistry usingSiC14 with organic dyes on powders, flat surfaces, and silica microstructures. Forthis work, quantification of PAS signal response to surface coverage is obtained bycomparing transmission and photoacoustic spectra for suitable samples. Photoacou9ticspectra, however, can be conveniently obtained for a wider range of coverages andfor coverages of nonuniform substrates such as microstructures.The utility of PAS for investigations of heterogeneous catalyst systems isillustrated by a study of reactions of molybdenum hexacarbonyl, Mo(CO)6, on varioussupport materials. On silica at -50'C, radiation-induced production of Mo(CO)5 onthe surface can be followed. With further irradiation, more highly coordinatelyunsaturated molybdenum species are generated. The effects of support compositionand preparation on these reactions have also been investigated in this study usingPAS.PAS can be used in the near-IR to examine vibrational overtone and combinationbands. Silica samples derivatized with ferrocene using DMP illustrate the utilityof this region. The DMP-derivatized silica shows both an aliphatic C,H-band at1.7. t and an aromatic C,H-band at 1.63 t.References1. A.B. Fischer, J.B. Kinney, R.H. Staley, and M.J. Wrighton, "Derivatization ofSurfaces via Reaction of Strained Silicon-Carbon Bonds. Characterization byPhotoacoustic Spectroscopy," J. Am. Chem. Soc. 101, 6501-6506 (1979).PR No. 122

Interfacial Chemistry

VI. INTERFACIAL CHEMISTRYAcademic Research StaffProf. R.H. StaleyGraduate StudentsR.W. Jones J.B. KinneyM.M. Kappes J.S. Uppal1. PHOTOACOUSTIC SPECTROSCOPY AND CHEMICALLY MODIFIED SURFACESJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)National Science Foundation (Grant DMR78-24185)Ralph H. Staley, Manfred M. Kappes, John B. KinneyWork has focused on using photoacoustic spectroscopy (PAS) to characterizethe results of chemical attachment reactions of molecules to surfaces and to studyheterogeneous catalyst systems and their reactions. PAS is being developed asa tool for the study of molecules adsorbed on surfaces. With the use of a Nicolet7199 Fourier-transform infrared spectrometer, PAS can be applied in the mid-infrared region to obtain vibrational information about the surface species. ThePA cell used is of our own design which allows the cell to be separated from themicrophone and loaded in an inert-atmosphere box or attached to a vacuum linefor sample preparation or reaction. The technique works best for studying sur-face species when the support is a high-surface-area powder (>10 m 2/g). Thistechnique has been used to study a variety of systems.A study of the adsorption of (COD)Pt(Me)2 on silica shows that the complexis only slightly perturbed by the silica. However, upon hydrogen exposure, themethyl groups are eliminated, presumably as methane, and the COD ligand is re-duced to some form of saturated hydrocarbon that does not readily pump off. Theplatinum is in the zero-valent state and is an active catalyst at this point, asis seen by the adsorption of carbon monoxide. Preliminary work on (COD)Pt(Me)2on alumina has shown that the complex reacts with the alumina, liberating methane.In another study, reactions of gases with supported metals have been exam-ined. These include the reactions of carbon monoxide and nitric oxide on platinumPR No. 123(VI. INTERFACIAL CHEMISTRY)supported on silica and alumina. Results are comparable to those obtained byother techniques. Reactions of hydrogen cyanide with platinum on silica andalumina, and silver on alumina, have also been studied. The carbon-hydrogen bondis cleaved and the surface is left covered with CN groups. Positions of the CNbands can be associated with different site structures for the CN groups on thesurface. This study is being expanded to include supported nickel, rhodium, andruthenium.Cobalt carbonyls attached to surfaces via silicone functionalities are alsounder study. The photochemistry of these systems is of particular interest.PR No. 123

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Interfacial Chemistry

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