Investigation of HNCO adsorption and hydrolysis on Fe-ZSM5

The adsorption of HNCO on Fe-ZSM5 was investigated in detail by DRIFT spectroscopy and compared to the adsorption on H-ZSM5, Al₂O₃, SiO₂, Fe₂O₃/Al₂O₃ and Fe₂O₃/SiO₂. At 150 °C, HNCO adsorbs dissociatively on Fe-ZSM5 producing principally isocyanate species (–NCO) adsorbed on Al and Fe sites. In the presence of water the hydrolysis of the –NCO groups to NH₃ was observed. Comparison of the DRIFT results with measurements of the catalytic activity of coated cordierite monoliths suggests that –NCO groups are likely intermediate species in the hydrolysis of HNCO over Fe-ZSM5.     

Fibrous long‐chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy,solid‐state CP/MAS 13C‐NMR,and X‐ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1‐ or 2‐h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid‐state CP/MAS ¹³C‐NMR (75.3 MHz). X‐ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X‐ray spectra or the unassigned C‐4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X‐ray diffraction data (4.1 nm). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1354–1365, 2000     

Surface characterization method of oxygen plasma-treated UHMPE fiber using DRIFT spectroscopy

The surface treatment and characterization of ultrahigh modulus polyethylene (UHMPE) fiber has been an important research subject. In this study, in order to investigate the oxygen plasma-treated UHMPE fiber according to the treatment time, diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was used as an analysis tool. The UHMPE fiber in a plain fabric was used for the surface analysis. The KBr overlay technique was efficient for enhancing the characteristic peaks from the UHMPE fiber surface. However, the KBr overlay made the comparison of the spectra among the UHMPE fiber samples difficult due to the different KBr overlay amount of each sample. In order to compare the relative peak areas of the oxygen plasma-treated UHMPE fiber according to the treatment time, DRIFT analysis was performed without KBr overlay under constant fiber orientation to remove the fiber orientation effect. The spectral subtraction was useful for investigating the minute change of the UHMPE fiber after the oxygen plasma treatment under the constant fiber orientation. The peak at 1896 cm⁻¹ was assigned to the crystalline combination mode of the UHMPE fiber and remained almost the same after the oxygen plasma treatment. This peak was used as an internal standard peak for the spectral subtraction and the peak area normalization. The relative peak areas in the DRIFT spectra of the UHMPE fiber were compared according to the oxygen plasma treatment time. The C=O group increases and the C—O group decreases as the oxygen plasma treatment time increases. The DRIFT analysis data of the oxygen plasma-treated UHMPE fiber correlated well with the electron spectroscopy for chemical analysis data and DRIFT spectroscopy is known to be useful for investigating the UHMPE fiber surface. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1117–1124, 1998     

SO2 promoted oxidation of ethyl acetate, ethanol and propane

The effect of SO₂ addition on the oxidation of ethyl acetate, ethanol, propane and propene, over Pt/γ-Al₂O₃ and Pt/SiO₂ has been investigated. The reactants (300–800 vol. ppm) were mixed with air and led through the catalyst bed. The conversions below and above light-off were recorded both in the absence and in the presence of 1–100 vol. ppm SO₂. For the alumina-supported catalyst, the conversion of ethyl acetate, ethanol and propane was promoted by the addition of SO₂, while the conversion of propene was inhibited. The effect of SO₂ was reversible, i.e. the conversion of the reactants returned towards the initial values when SO₂ was turned off. However, this recovery was quite slow. The oxidation of propane was inhibited by water, both in absence and presence of SO₂. For the silica-supported catalyst no significant effect of SO₂ could be observed on the conversion of ethyl acetate, ethanol or propane, whereas the conversion of propene was inhibited by the presence of SO₂. In situ FTIR measurements revealed the presence of surface sulphates on the Pt/γ-Al₂O₃ catalyst with and after SO₂ addition. It is proposed that these sulphate groups enhance the oxidation of propane, ethyl acetate and ethanol by creating additional reaction pathways to Pt on the surface of the Pt/γ-Al₂O₃ catalyst.     

2. Sensitized degradation of chlorophenols on iron oxides induced by visible light: Comparison with titanium oxide

The sensitized photocatalytic degradation of mono-, di- and trichlorophenols on iron oxides aqueous suspensions of -Fe₂O₃ and -FeOOH is reported in detail. The degradation of these compounds followed pseudo-first-order kinetics when -Fe₂O₃ was used as photocatalyst. -FeOOH was found to be inactive for chlorophenols degradation with the exception of 2,4-dichlorophenol (2,4-DCP) where a modest effect was observed. The formation of a surface complex by the chlorophenols with the iron oxide and the solubility of the particular chlorophenol in aqueous solution were observed to be the controlling parameters during the photodegradation. The results obtained with the most active catalyst -Fe₂O₃ are compared with TiO₂. Total mineralization of chlorophenols was observed on TiO₂ while on -Fe₂O₃ only partial mineralization was observed. In either case, the intermediates produced in solution during the photodegradation were found to be significantly more biodegradable than the initial compound. For mono-, di- and trichlorophenols the overall photocatalytic degradation was observed to increase in the order: 2,4,6-trichlorophenol (2,4,6-TCP)<2,3-dichlorophenol (2,3-DCP)<2-chlorophenol (2-CP)<2,4-DCP. The former sequence shows that the recalcitrant 2,4-DCP degrades more rapidly than other chlorophenols tested during this study. The photodegradation of chlorophenols on -Fe₂O₃ and TiO₂ proceeds mechanistically through para-hydroxylation of the initial compound as suggested by the intermediates found by high-pressure liquid chromatography HPLC during the course of the degradation.     

SO2 oxidation over the V2O5/TiO2 SCR catalyst

The effects of V₂O₅ loading of the V₂O₅/TiO₂ SCR catalyst on SO₂ oxidation activity were examined by infrared spectroscopy (DRIFT) and SO₂ oxidation measurement. Vanadium oxide added to the catalyst was found to be well dispersed over the TiO₂ carrier until covered with monolayer V₂O₅. The rate of SO₂ oxidation increased almost linearly with V₂O₅ loading below the monolayer capacity and attained saturation with further increase. The hydroxyl groups bonded to vanadium atoms, V–OH, might be altered by SO₂ oxidation. Both V=O and V–OH groups are likely involved in the adsorption and desorption of SO₂ and SO₃.     

DRIFT studies of thick film un-doped and Pd-doped SnO2 sensors: temperature changes effect and CO detection mechanism in the presence of water vapour

Diffuse reflectance infrared Fourier transform measurements were performed on tin oxide based thick film gas sensors operated in normal working conditions. We characterised SnO₂ sensors at different temperatures between room temperature and 300 °C. The results show the presence of different surface OH groups as well as coordinated water on the SnO₂ sensor surface. Their intensity changes with temperature. During the temperature cycles the bands’ peak positions are reversibly changed but their intensity is not. CO measurements were performed at 300 °C at different humidity levels (0 and 50% r.h.) on un-doped and Pd-doped sensors. In the presence of CO we observed in the spectra: a decrease of the OH groups on the SnO₂ surfaces, the appearance of gaseous CO₂ and CO in the pores of the sensitive layer and an increase of hydrated protons and of the free charge concentration. The effects are dramatically influenced by the water vapour concentration, temperature, dopands (Pd) and can be correlated with simultaneously performed sensor resistance measurements.     

FTIR Spectroscopic Study of CO Adsorption on Cu/SiO2: Formation of New Types of Copper Carbonyls

The nature of zinc ions in ZnHZSM-5 zeolite prepared by incipient wetness impregnation was studied by DRIFT spectroscopy using dihydrogen adsorbed at low temperature as a molecular probe. The results obtained indicate the appearance of low-coordinated zinc ions following dehydroxylation at high temperature. It is concluded that the ions that most strongly perturb adsorbed hydrogen are localized on the surface of nanometric ZnO clusters that are formed in the channels of the zeolite framework upon high temperature pretreatment. This was demonstrated by the inhibition of dihydrogen adsorption by high temperature sulfidation of the zeolite with H₂S. The latter presumably converts ZnO particles into ZnS clusters. This was also confirmed by UV diffuse reflectance spectra of the sulfided samples. By contrast, sulfidation did not influence DRIFT spectra of hydroxyl groups in either HZSM-5 or HY zeolites, indicating that substitution of framework oxygen by sulfur does not occur in these materials.     

Assessment of water quality effects on flotation of copper–cobalt oxide ore

Results from lab scale flotation show that when process water was re-used copper and cobalt recovery from an oxidized ore decreased respectively with 25% and 30% at the rougher stage bringing lower grade concentrate as well. The presence of thiosulphate ions contributed to slow down of NaHS consumption during sulphidisation of pure malachite and hindered collector adsorption. Elevated concentration of thiosulphate ions affected malachite surface properties and induced dissolution effects. DRIFT spectroscopy on activated malachite enabled to reveal the effects of thiosulphate ions presence with hydrophilic species being identified.     

Spectroscopic and Kinetic Analysis of a New Low-Temperature Methanol Synthesis Reaction

The spectroscopy and kinetics of a new low-temperature methanol synthesis method were studied by using in situ DRIFTS on Cu/ZnO catalysts from syngas (CO/CO₂/H₂) using alcohol promoters. The adsorbed formate species easily reacted with ethanol or 2-propanol at 443 K and atmospheric pressure, and the reaction rate with 2-propanol was faster than that with ethanol. Alkyl formate was easily reduced to form methanol at 443 K and 1.0 MPa, and the hydrogenation rate of 2-propyl formate was found to be faster than that of ethyl formate. 2-Propanol used as promoter exhibited a higher activity than ethanol in the reaction of the low-temperature methanol synthesis.