Search

Strong Lewis acidity of a phase-pure γ-Ga2O3 was studied by the adsorption of CO at ambient temperature, with the combined use of adsorption microcalorimetry and in situ Fourier transform infrared ...

In this work, the surface properties of imogolite are studied, in terms of type, acidic strength, accessibility and stability of hydroxyls groups. Imogolite nanotubes present interesting surface features, in that the outer surface is covered by Al(OH)Al groups and an inner surface lined by isolated ≡SiOH groups. The knowledge of the acidic strength and of the actual accessibility, for example to reactants in a acidic-catalyzed reaction, is of paramount importance for any practical application. Being an hydrated alumino-silicate, the behaviour of imogolite surface resulted to be very sensitive to the pre-treatment temperature: experimental results showed that molecular water is removed only at 300°C, rendering inner silanols accessible to probes like CO, methanol and even phenol. Inner silanols are as acidic as those at the surface of amorphous silica, but the presence of plenty of them at the inner surface enhance the interaction with the adsorbed molecules, thus hindering diffusion. At higher pre-treatment temperatures (500°C), the nanotubes structure is lost, with formation of a lamellar phase, which, interestingly, shows new stronger acidic properties, resembling those of amorphous alumino-silicates with high Al content.

Pure and PO 4 -doped aluminas (≍ 3% P 2 O 5 ), pretreated at three different temperatures (773, 1273, and 1473 K), have been compared by XRD, TEM, and FTIR spectroscopy. The addition of phosphates does not modify the phase transition of low-temperature spinel aluminas (γ-Al 2 O 3 ) to high-temperature spinel aluminas (δ, θ-Al 2 O 3 ), and delays somewhat the phase transition from spinel alumina to the corundum phase (α-Al 2 O 3 ). Phosphates have a positive effect on surface area and porosity only for the corundum phase obtained at T ≥ 1450 K, in which the particles morphology is modified with respect to pure (α-Al 2 O 3 ). The effect of PO 4 -doping is appreciable on surface basicity and acidity. The weak basicity of alumina is gradually eliminated, with increasing firing temperature. The presence of phosphates increases the strong surface acidity of aluminas: phosphates tend to collect preferably on the flat patches of regular crystal planes, and so doing decrease the amount and increase the strength of the Lewis acid sites (coordinatively unsaturated (cus) Al IV ions) present on the regular crystal planes. Meanwhile, the presence of phosphates produces an appreciable increase of the number of strong cus Al IV Lewis acid sites present in crystallographically and/or coordinatively defective configurations. When the bulk transition to α-Al 2 O 3 has occurred in systems treated at T ≥ 1400 K, the samples retain surface properties reminiscent of those of the transition alumina phases. The diverse opinion of investigators that phosphates act toward alumina as phase stabilizing needs some corrections and additions: the positive role of phosphates on the alumina support implies the stabilization of higher amounts of the strong Lewis acid sites that are most likely to be important in catalytic applications.

Chars prepared by pyrolyzing polyvinyl chloride, polyvinyl bromide, and polyvinyl fluoride in vacuum were oxidized in pure 0 2 at 150 Torr over the 100–600°C range. The chars were chosen to be representative of each of the different stages of the degradation and carbonization process of the specific polyvinyl halide and/or the group as a whole. Reactions leading to the formation of surface oxidic species were followed with infrared photothermal beam deflection spectroscopy and the results discussed in relation to the nature of the individual char and its extent of carbonization. Some band assignments to specific surface species were made, and the evolution of these bands was followed and discussed in the context of the surface properties of the char precursor. Low temperature chars ( 450 °C resulted in the burn-off of the chars and the accompanying loss of acidic carbonylic species.

Fourier transform photothermal beam deflection spectroscopy was used to record the spectra of chars produced by heating in vacuo pure polyvinylidene chloride (PVDC) and the copolymer Saran over the 100–690°C range. The infrared spectra obtained provide direct information about the degradation and subsequent carbonization of PVDC and Saran. Pyrolysis of both homopolymer and copolymer at T = 200°C results in the destruction of the original ordered vinylidene structure and there is spectroscopic evidence for the formation of polyenic sequences. At T>200°C the spectra show the development of an increasingly aromatic system with rings containing evidence of chlorine substitution. As pure polyvinylidene chars contain 50% less hydrogen than their polyvinyl counterparts, the spectra of chars obtained at T>400°C show little vibrational structure in the region >2000 cm−1, and at degradation temperatures >500°C no vibrational features are observable over the entire 4000 - 500 cm−1 range. In contrast, the inclusion of only a small percentage of vinyl monomer in the copolymer Saran results in chars whose spectra exhibit vibrational features up to degradation temperatures of 690°C. The spectroscopic character of PVDC and Saran chars and their oxidation are discussed in detail. In addition, these results are compared and contrasted with earlier analyses of the chars of polyvinyl chloride and polyvinylidene fluoride.

Infrared photothermal beam deflection spectroscopy was used to record spectra of pyrolyzates produced by heating an aliphatic allyl polycarbonate in vacuo and in the air. It was found that this resin would not char to an appreciable extent upon vacuum pyrolysis unless it had been first subjected to an initial oxidation at low temperature (250°C). The char derived after such a treatment, and after its subsequent pyrolysis at high temperature, exhibits all the infrared spectral characteristics associated with the intermediate-temperature carbons.

Fourier transform photothermal beam deflection spectroscopy was used to examine chars produced by heating pure polyvinylidene fluoride (PVDF) in a N2 stream at temperatures ranging from 300 to 700°C. The infrared spectra obtained provide direct information about the destruction of the original polymer structure as well as its carbonization. PVDF exhibits a high thermal stability, characteristic of polyvinyl fluorides and spectroscopic evidence of the onset of degradation occurs near 300°C. Increasing the pyrolysis temperature results in a complex degradation process and a pyrolytic residue made up of largely aliphatic and fluoro-aromatic structures. The loss of most of the hydrogen-containing groups at temperatures in excess of 400°C results in a spectrum showing no vibrational features at wavenumbers >2000 cm−1 and a high temperature profile quite different from those previously observed for the polyvinyl chloride, bromide and fluoride chars. The possible mechanisms for the degradation of PVDF as suggested by the spectroscopic evidence is discussed in detail.

Although the degradation of polyvinyl fluoride (PVF) has been studied, emphasis has been placed on weight loss analyses and the study of the gases evolved during the degradation process. Little is currently known about the nature of the pyrolytic residue or of the chars which are formed during thermal degradation at higher temperatures. Fourier transform beam deflection spectroscopy was used in this study to examine chars produced by heating pure PVF in vacuum at temperatures ranging from 110°C to 685°C. The infrared spectra of the chars provide direct information about the degradation and subsequent carbonization of PVF. PVF exhibits a higher thermal stability than the polyvinyl halides which we have previously examined and consequently the first spectral evidence of degradation is not observed until 300°C. This higher temperature, which accompanies the initial loss of fluorine, suppresses the formation of long polyenic sequences and results in an overall degradation mechanism which consists of overlapping reactions involving polyene formation, chain scission, cross-linking and intramolecular cyclization. At temperatures above 500°C the aliphatic and aromatic structures formed during the first stages of the degradation process are replaced by a growing aromatic network. The spectral evidence for the occurrence of many of these reactions is presented in detail.

Series of infrared spectra were recorded of chars produced by heating a pure bisphenol-A polycarbonate resin (PC) in vacua at successively increasing temperatures, up to 750°C. FT-IR photothermal beam deflection spectroscopy was used. PC, after remaining essentially intact over a wide range of temperatures, underwent massive and dramatic changes upon heating in a narrow temperature interval (440–490°C). Thermal branching and cross-linking occurred near 440°C with the formation of diaryl ether, ester and unsaturated hydrocarbonaceous bridges. Small, still discrete aromatic entities were formed on pyrolysis above 490°C. Fusion of the aromatic rings into larger polyaromatic structures, however, occurred to a significant extent only at 590°C, when the polymeric network collapsed completely; all aliphatic bridges were destroyed and the oxygen bridges were incorporated in the polyaromatic domains which were formed. The resulting char was similar to other intermediate temperature chars. The continuum of the carbon absorption extends throughout the spectral region at 750°C.

IR photothermal beam deflection spectroscopy was used to record IR spectra of chars, produced by the in vacuo pyrolysis of a polycarbonate resin (PC), at several stages of oxidation. The high-temperature chars seem to be more susceptible to oxidation than the low-temperature PC chars. This behavior is quite unlike that of coals, cellulose based chars, and other carbons. Oxidation of the low temperature chars proceeds mainly through attack on the hydrocarbonaceous side chains and the elimination of carbonate functionality, accompanied by an extensive formation of benzophenone, lactones, and acidic carbonylic species. However, the chars obtained at temperatures higher than 590°C, when polyaromatic domains first form to a significant extent, exhibit the normal oxidation behavior found with chars derived from several types of precursors.

In situ FTIR spectroscopy and adsorption microcalorimetry have been employed to study the adsorption/desorption of 2,6-dimethylpyridine (2,6-DMP) on different zirconia and sulfated zirconia (SZ) systems. Adsorption/desorption experiments were carried out at 343 K (beam temperature for all IR experiments) and at 423 K. The adsorbents were (i) a (mainly) monoclinic zirconia, (ii) a crystallographically pure tetragonal zirconia, phase stabilized by formation of a solid solution with 3 mol % Y2O3, (iii) monoclinic sulfated zirconia (m-SZ) and tetragonal sulfated zirconia (t-SZ), both noncalcined and calcined at 923 K, obtained by direct sulfation of the two crystalline ZrO2 specimens, and (iv) two t-SZ specimens (also noncalcined and calcined at 923 K), obtained through the “conventional” sulfation procedure carried out on an amorphous hydroxide precursor and leading, upon thermal treatment at T > 823 K, to crystalline t-SZ. The adsorption/desorption of 2,6-DMP turned out to be a valuable probe for both Brons...

Acetonitrile and adamantane-carbonitrile form hydrogen-bonded adducts with both silanols and Bronsted acid sites of zeolites. The corresponding changes in the O-H stretching vibration render the zeolite surface IR-readable. The combined use of both probe molecules helps to differentiate between internal and external OH groups of medium pore zeolites, since acetonitrile can enter the zeolite channels while adamantane-carbonitrile cannot. The method was demonstrated by analysing the interaction of both probe molecules with H-ZSM-5 samples which were synthesized under different conditions. It was shown that a sample prepared in the presence of a template agent (tetrapropylammonium bromide) had a proportion of internal silanols much higher than that found for an analogous H-ZSM-5 sample synthesized by a template-free route. Bridged Si(OH)Al groups (Bronsted acid sites) were found to be located mainly at the internal surface of the zeolites, although the sample prepared using the template agent showed some evidence for the presence of a small proportion of these acid sites at the external surface.

In the last decade a great deal of work has been devoted to the characterization of Yttriastabilized tetragonal ZrO2 (YSTZ), because of its large use as a ceramic material. Many efforts have been made to evaluate some macro- and mesoscopic characteristics of YSTZ, such as those obtained by mechanical tests (e. g., shrinkage, sinterability, KIC, specific surface area SSA, etc), whereas only little attention has been focused so far on the evolution of the nanostructural and surface reactivity features of the starting powders. It is normally observed that YSTZ precursors, that have been preliminarly treated in different conditions, exhibit quite different sintering behaviours.

Three specimens of crystalline AlF3, coming from different preparation routes, have been examined: no major differences were found in the spectral region of the (ν3) fundamental mode, whereas the preparation process was observed to introduce appreciable differences in the background spectra that were ascribed to different bulk and surface impurities. Oxidic islands exist both in the bulk and at the surface of all preparations and when AlF3 is derived from non-oxygen-containing precursors. In the latter case, species containing NHx moieties exist, both in the bulk and at the surface. The surface hydrated layer of AlF3 is made up of an extensive ‘regular’ component (i.e. a large amount of undissociated water molecules, coordinated to unsaturated surface AlVI cations), and of an ‘anomalous’ component (i.e. some OH groups that are eliminated upon vacuum activation at relatively low temperatures). The adsorption of pyridine on samples activated by vacuum treatment at temperatures in the range 300–673 K indicates that on all specimens there are variable amounts of ‘irregular’ surface cations [i.e. coordinatively unsaturated surface Al ions with (quasi-)tetrahedral coordination], some of which are strong enough as Lewis-acidic centres to adsorb CO at ambient temperature. Coordinatively unsaturated surface Al ions with the ‘regular’ octahedral coordination are very weakly acidic, as revealed by the end-on adsorption of CO2 at 300 K and by CO uptake at ca. 78 K.

High resolution transmission electron microscopy (HRTEM) shows that TiO 2 microcrystals obtained by flame hydrolysis of TiCl 4 exhibit a virtually perfect crystalline habit with only a few crystallographic planes most abundantly exposed. CO adsorbs at 77 K on the Ti 4+ five-coordinated ions emerging on these faces yielding, at maximum coverage, a strong ir band at 2179.5 cm −1 . The very low hand-band width of this peak ( −1 ) indicates that the adsorbed layer possesses a high degree of bidimensional order. By decreasing the CO coverage the main peak becomes broader and shifts gradually to 2192.5 cm −1 : this is due to changes in the lateral (dynamic and static) interactions. Other less intense peaks can be related to CO adsorbed on sites of higher Lewis acidity, to CO hydrogen bonded to residual OH groups and to the formation of tilted species.

Infrared photothermal deflection spectra were recorded of single crystals and powders of calcite and (NH 4 ) 2 SO 4 , SiC powders, of a 58% Ni-on-kieselguhr catalyst, and of oxidized carbon. The photothermal effect was diminished in regions of strong reflection and absorption so that distortions appeared in absorption bands. Specular reflection thus can effect photothermal or photoacoustic spectra and the distortions cannot be corrected unless all optical parameters of the materials are known. Similarly, diffuse reflection enhances the photothermal effect. Thus, the widely-held generality that the photoacoustic spectroscopy of solids is unaffected by reflection is not correct.

The new technique of infrared (IR) photothermal beam deflection spectroscopy (PBDS) is outlined and measurements of IR spectra of solids over the range 3950 - 450 cm −1 made with an interferometer coupled with a detector which senses the photothermal effect by the deflection of a He/Ne laser beam are described. PDS is a general technique and requires no sample preparation. All that is needed is a simple device to hold the sample at the IR focus. The sample must have a flat spot about 2 mm in diameter accessible to the IR and laser beams. As no sample cells per se are needed, the solid to be examined can be very large, so that selected areas on an entire catalyst pellet can be examined. IR spectra can also be recorded of adsorbed species at sub-monolayer coverage and, significantly, this can be done under the rigorously controlled conditions normal to surface studies. Adsorbents and catalysts which scatter and/or absorb IR strongly can be studied, e.g. catalysts with high metal contents, carbons and chars, and carbon-supported metal catalysts. Such materials would be impossible to examine by the conventional IR transmission/absorption techniques. Examples are given, such as spectra of CO chemisorbed on 50 wt.% Ni on carbon and of surface species on silica in a spectral region normally not accessible to IR spectroscopy.

Fokrier transform photothermal beam deflection spectroscopy kas ksed to examine chars prodkced by heatink pkre polyvinyl chloride (PVC) in dynamic vacka at temperatkres rankink from the ambient to 650°C. The infrared spectra obtained provide direct information abokt the destrkction and carbonization of PVC. Initially, polyenic strkctkres form at T ≦ 240°C. These are destroyed at 240–450°C, and polyaromatization alonk kith loss of fknctional krokps occkrs at T > 450°C. The mechanisms of PVC dekeneration and of char formation are described and disckssed in detail.

The heating of samples during infrared (IR) transmission/absorption spectroscopic measurements has been known and of some concern for many years. Emission of radiation by the sample can cause spectral artifacts, and sample heating is of particular importance for surface studies at or near ambient temperatures because surfaces may become altered by the desorption of gases. Such effects, discussed elsewhere,1,2 must be considered for photoacoustic spectroscopy (PAS).

The pyrolysis in vacuum of cellulose containing 5 wt. % of KHCO3 (KHC) was followed by IR photothermal beam deflection spectroscopy, and compared with observations made with pure cellulose (PC) [Carbon 21, 283(1983)]. The KHCO3, and KOH and K2CO3 formed from it, drastically altered the cellulose carbonization and the subsequent oxidation of the KHC chars. KHC became charred at 140 °C and the cellulose disrupted at 220 °C. The surface layer was a mixture of weak acid K salts. K2CO3 was not formed until 310 °C and persisted until about 500 °C, when metallic K was evolved. Unlike PC, the surface layer contained no aromatic CH structures. The carbonization of KHC proceeded more rapidly and to a greater extent than with PC. The oxidation of KHC chars was also markedly affected; burn-off occurred at much lower temperatures, and the gasification temperature range was narrower, than with PC chars.

Infrared spectra were recorded of the chars produced by pyrolyzing a Novolac phenol-formaldehyde resin in vacuum and in nitrogen, using photothermal beam deflection spectroscopy. The two pyrolysis techniques led to the same results. Thermal branching and cross-linking occurred near 350°C, with the formation of diphenyl ether structures. These reactions continued at higher temperatures when aryl-aryl ethers were formed. Autooxidation is not an important degradation pathway. Although some changes occur, the polymer network remains essentially intact until 500°C, the aromatic systems being held apart and stabilized by aliphatic bridges. In the 500–560°C range, however, drastic changes occur in that the network collapses, aliphatic bridges are destroyed, hydrocarbonaceous residues are eliminated and those remaining are altered, polyaromatic domains form, and the resulting char is much like other intermediate temperature chars.

The pyrolysis of cellulose in vacuum from 22 to 765°C was followed by IR photothermal beam deflection spectroscopy. Series of spectra recorded at various stages of pyrolysis showed that although the main decomposition occurred near 300°C, some decomposition occurred as low as 190°C with the formation or highly absorbing aromatic systems. Mixtures of predominantly aliphatic material predominate in the 300–400°C range but decline in extent to be replaced by mixtures of aromatic nature above 500°C. Further degassing causes discrete spectral features to decline and disappear near 700°C; a continuum absorption remains. Band assignments are discussed. In particular, the 1600 cm −1 band of spectra of carbons is shown by isotopic study not to be ascribed to carbonyls. but is thought to be a C = C mode made IR active by asymmetry caused by bound oxygen.

Infrared (IR) photothermal beam deflection spectroscopy (PBDS) is briefly described and some of its applications to studies of carbons and highly scattering materials are reviewed. PBDS is especially useful for the study of materials which absorb IR radiation very strongly or act as strong IR scatterers, so that conventional IR techniques fail. Application of PBDS to study the thermal degradation of a phenol-formaldehyde resin, the reaction of NH3 and H2O with the surfaces of intermediate-temperature chars, the effect of Fe3+ on the charring of cellulose, the dehydration of titanyl sulphate, and TiO2 pigments, are described.

Infrared spectra of areas about 2.5 × 1 mm on the surfaces of fossil plant or animal remains can be recorded nondestructively with the use of photothermal beam deflection spectroscopy. Samples need not be removed from the fossil, which may remain on or in its matrix, as long as a portion of the fossil's surface is accessible to the analyzing beams. The technique is potentially valuable for the examination of special samples of palaeontological and archaeological interest.

Nearly three decades have passed since Eischens et al. 1 measured the infrared bands of CO chemisorbed on Cu, Ni, Pt and Pd, and their assignments, unscathed by time and criticism, have prompted a great deal of infrared work on the interactions of CO with a wide variety of adsorbents. CO adsorption, followed by a variety of infrared techniques, has now become a valued conventional tool for surface studies. The C-O stretching bands of chemisorbed CO yield data about band frequency, half-width, contour and intensity, as well as band shifts and intensity changes when some parameter is changed, which provide information about the structure of the chemisorbed species and permit deductions to be made concerning the adsorbate-adsorbent interaction and the nature and properties of the surface. However, we now find and show that under certain conditions such data, measured by the conventional transmission/absorption (T/A) techniques, can be susceptible to errors and artifacts stemming from the measurement...

FTIR photothermal beam deflection (PBD) spectroscopy was used to record PBD spectra of IR-absorbing gases in presence of IR-absorbing and non-absorbing solids. The presence of the solid, IR-absorbing or not, causes asymmetry at the juncture of the IR and probe laser

Infrared Fourier transform photothermal beam deflection spectroscopy (PBDS) is briefly outlined. It involves heating a surface by the photothermal effect, using infrared (IR) radiation from a scanning interferometer; energy is transferred to the gas above the surface and the resulting refractive index gradient in the gas is detected by observing the deflection of a laser beam grazing the solid's surface; the deflection is related to the IR radiation which is absorbed, so that the Fourier transform of the deflection signal results in the IR spectrum. PBDS is especially useful for materials which scatter and/or absorb IR radiation so extensively that conventional transmission/absorption techniques are not possible. A variety of examples of applications are given, including spectra of polymers, floor tile, polyester thread and fabric, leather, cellulose, paper, lichen and bone.

FT-IR photothermal beam deflection spectroscopy (PBDS) is truly nondestructive in that none of the sample preparation methods needed for the IR examination of solids are mandated. Such nondestructive examination is, however, inefficient—in that long scanning times are frequently needed—and is not really required with many samples. If it is permissible to subject the sample to a simple hand grinding, efficiency can be greatly improved. Sample preparation and handling are discussed, and the peculiarities of certain samples are described. Particular emphasis is placed on the necessity of proper sample handling for surface studies, data of the vacuum pyrolysis of polyvinyledene being used as example.

The pyrolysis of an NO2-oxydized cellulose (NOC) in vacuum from 22 to 700°C was followed by IR photothermal beam deflection spectroscopy. Series of spectra were recorded at various stages of pyrolysis and compared with and contrasted to similar data previously obtained with cellulose. Also, NOC-derived chars were oxidized, and the effects of treating NOC and NOC char with KOH were observed. The detailed IR spectroscopic data indicate that NOC degrades more easily than cellulose and yields chars that possess different functional groups than cellulose chars, up to charring temperatures of near 500°C. Above that temperature the chars have similar chemical and physical properties.

Silica can be dehydroxylated by treatment with HSiCl 3 at 325°C. The resultant SiOSiHCl 2 monolayer will sorb pyridine at 22°C, forming Lewis, hydrogen-bonded and Bronsted surface species. The formation of the Lewis surface species was accompanied by a marked decrease of the intensity of the SiH stretching vibration band of the surface silane groups. All sorbed pyridine species are weakly held to the surface and could be removed by degassing briefly at 50°C. Infrared Fourier transform spectroscopy was used to follow the reactions.

The new technique of infrared photothermal beam deflection spectroscopy (PDS) is outlined, and measurements made with an interferometer coupled with a detector which senses the photothermal effect by the deflection of a laser beam are described. PDS is a general technique and requires no sample preparation or sample cells per se. Consequently, thick surface layers can be examined in situ, even with very large objects. An example of the infrared examination of the corrosion layer on a massive strap from a lead storage battery is given. Infrared spectra can also be recorded of adsorbed species, and most significantly, this can be done under the rigorously controlled conditions normal to surface studies. Spectra are shown of cellulose chars, and of CO chemisorbed on a 50 wt% nickel-on-carbon catalyst, “black” samples which would be impossible to examine by conventional means. PDS is thus an important and versatile technique for surface studies.

Since what appears to be the first infrared (IR) observation of a char by Kmetko in 1951,1 IR spectra of coals, chars and various carbon materials have been invariably shown to have a more or less intense band near 1600 cm−1. A variety of suggestions has been made concerning the cause of the band but the assignments have been in dispute and remained controversial for thirty years.

IR photothermal beam deflection spectroscopy (PBDS) was used to record spectra of intermediate-temperature carbon materials having greatly different properties and origins. A good charcoal, anthracite coal, bituminous coal, and two Chromatographic carbons were studied in a cell under the controlled conditions required for surface studies. PBD spectra recorded after various heat treatments in vacuum, and after oxidation, were compared with those of cellulose-derived chars. IR data concerning the degree of carbonication, the formation and changes of the various species making up the surface layers, and inorganic materials within the carbons, were obtained easily and are discussed. IR-PBDS is a valuable technique for the study of intermediate carbons and their reactions.

The feasibility of carrying out infrared studies of intermediate chars, i.e., chars produced by pyrolysis of carbonaceous materials in the 450°–650°C range, is examined. Infrared spectra of such materials can be recorded using photothermal beam deflection spectroscopy (PBDS). Four different chars produced by pyrolyzing different materials in vacuo were examined after formation and after oxidation at 400 °C. Interpretation of the various data concerning the surface species which were detected indicates that intermediate chars of different provenance are rich in surface groupings the nature of which is largely independent of the nature of the starting materials. However, the various chars show great differences after oxidation ; these can be followed in great detail via the PBDS technique, which permits the examination of opaque samples under the controlled conditions required for surface studies.

Carbons prepared by charring cellulose in vacuum were oxidized under the conditions leading to the formation of acid or basic carbons. The reactions were followed with IR phothermal beam deflection spectroscopy. The oxidation of chars at temperatures leading to the formation of acid carbons resulted in the formation of several surface species to which acid properties may be ascribed. Some band assignments to definite surface structures were made. Spectra were recorded for the first time of high temperature carbons oxidized at the high temperatures leading to the formation of basic carbons, and the interconversion of acid and basic carbons could be followed. No oxygen-containing species to which basic properties could be attributed were observable.

The pyrolysis in vacuum of cellulose containing 5 wt.% of NaCl (NCC) was followed by i.r. photothermal beam deflection spectroscopy, and compared observations made with pure cellulose (PC) [Carbon21, 238 (1983)]. Although the overall aspects of NCC and PC pyrolysis were similar, NaCl accelerated the cellulose decomposition, the relative amounts of aliphatic and aromatic residues were changed, and i.r.-detectable species disappeared about 100°C lower than with PC, all implying changes in the decomposition and charring mechanisms. The reactions of NCC chars with O2 was also followed and compared with those of PC chars. NaCl caused the ratios of oxidation products to change (some band assignments are discussed) but the behavior of NCC chars produced at 650°C, when NaCl evaporated, was similar to high-temperature PC chars.

Photothermal bean deflection spectroscopy (PBDS) was used to record infrared (IR) spectra of monolayers of pyridine adsorbed on particulate adsorbers which absorb IR radiation weakly, and of pyrene adsorbed on medium- and high-temperature carbons which are very strong IR absorbers. The various results show that although some IR data about surface layers on weak absorbers can be obtained, the data are generally inferior in quality than those obtainable with IR transmission/ absorption measurements. PBDS results decrease in quality as the transparency of the sample increases. Increasing the specific surface area and the degree of compaction of the sample can lead to an improvement, but a high surface area per se is neither a necessary nor sufficient condition. The scattering of IR radiation appears to be the most important of the parameters which can affect the quality of the PBD spectra, and a favourable combination of surface area, compaction and especially scattering effects can result. In general, the PBD technique has little to offer for use with non-scattering weak absorbers, but can be usefully applied with highly-scattering weak absorbers. With the other extreme type of sample, the very strong absorbers, PBDS has been used to observe monolayers of pyrene on medium- and high-temperature carbons. Although the spectra of the adsorbed species are relatively poor in comparison to those obtained with medium or strong absorbers, improvements in technique seem possible, so that PBDS will become a unique method for the study of surface effects with very strong absorbers.

FT-IR photoacoustic (PA) and also photothermal beam deflection (PBD) spectra were recorded with the same particulate samples (graphite, charcoal, aspirin, and silica) under the same conditions in order to compare the quality of the spectra obtainable with the two techniques. A PA cell fitted with windows for the PBD laser probe beam was used, and PA and PBD spectra of each sample were recorded at 8 cm−1 resolution at each of the four different interferometer scan velocities. Although the overall aspects of FT-IR/PA and FT-IR/PBD spectra are the same, the signal-to-noise ratios of PA spectra are appreciably better than those of PBD spectra because PBD detection is more prone to disturbance by vibration than is PA detection. Absorption bands appear at the same wavenumbers in PA and PBD spectra. However, the relative intensities of bands of PBD spectra depend on the absorptive properties of the powdered solids; with weak absorbers, some bands may not be detected at all. PAS can be used with all powders. PBDS is of little or no use for the examination of weakly absorbing powders unless they scatter IR radiation extensively.

The infrared (IR) study of surface species and reactions occurring on solids has contributed markedly to our understanding of surface chemistry and heterogeneous catalysis, and a wide variety of solids has been examined. However, an entire class of catalysts consisting of metal dispersed on carbon has never been studied because the carbon catalyst support absorbs IR radiation so strongly in even the thinnest practical layers that conventional IR techniques fail. As IR data would be helpful in understanding how such catalysts function, we have explored the feasibility of examining carbon-supported catalysts with photothermal beam deflection spectroscopy (PDS) and describe the first IR spectra ot surface species on a Ni-on-carbon catalyst.