The interaction of alumina with HCl: An infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering study

The interaction of HCl with an η-alumina catalyst has been investigated by a combination of diffuse reflectance infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering (INS) spectroscopy. Infrared spectra provide evidence for dissociative adsorption of HCl and for a process in which hydroxyl groups terminally bound to Al are replaced by chlorine. Temperature-programmed desorption experiments show HCl to desorb over the temperature range 350–>970 K, indicating dissociative HCl adsorption to occur on a wide range of active sites. INS experiments show the residual alumina hydroxyl groups to exhibit an out-of-plane deformation feature, γ(OH), at ca. 200 cm⁻¹, while the in-plane deformation mode, δ(OH), is seen at ca. 1000 cm⁻¹. The formation of new surface hydroxyl groups via the adsorption of hydrogen chloride yields a δ(OH) feature that can be resolved into two bands at 990 and 1050 cm⁻¹. Hydrogen bonding within the alumina/HCl system is responsible for the observation of an Evans transmission window in the infrared spectrum, that occurs via a Fermi resonance interaction between (i) the ν(OH) mode of hydrogen bonded hydroxyl groups and chemisorbed water with (ii) the overtone of the δ(OH) mode of surface hydroxyl groups. The INS technique is able to discriminate among different hydroxyl group bonding geometries on the basis of the local symmetry of the active sites.     

Hydrogen production from ethanol over bimetallic Rh-M/CeO2 (M = Pd or Pt)

The reaction of ethanol for the production of hydrogen has been studied over a series of metal supported CeO₂ catalysts. The study is conducted by TPD, steady state reaction, XPS, TEM, and infrared spectroscopy. TPD gave evidence for the role of Rh in dissociating the carbon–carbon bond needed for efficient production of hydrogen molecules. IR of CO adsorption at 90 K revealed that Rh particles are most likely in very small clusters as evidenced by a single OC–Rh IR band at 2020 cm⁻¹. TEM did not show conclusive evidence for the presence of the metal on-top of the CeO₂ support, yet the Rh-Pd/CeO₂ used catalyst has features that might be attributed to epitaxial growth of the noble metal along the (1 1 1) surface of the CeO₂ support. Considerable reconstruction of the CeO₂ support is seen for the used catalysts, in addition. Reforming of ethanol to hydrogen using (3 moles of water per mole of ethanol) was very efficient particularly above 650 K where hydrogen selectivity reaches 60 vol.%. At these temperatures hydrogen production from reforming of methane takes place.     

In situ FTIR study on NO reduction by C3H6 over Pd-based catalysts

The reaction mechanism of the reduction of NO by propene over Pd-based catalysts was studied by FTIR spectroscopy. It was observed that the reaction between NO and propene most probably goes via isocyanate (2256–2230 cm⁻¹), nitrate (1310–1250 cm⁻¹) and acetate (1560 and 1460 cm⁻¹) intermediates formation. Other possible intermediates such as partially oxidized hydrocarbons, NO₂, and formates were also detected. The reaction between nitrates and acetates or carbonates reduced nitrates to N₂ and oxidized carbon compounds to CO₂. In situ DRIFT provides quick and rather easily elucidated data from adsorbed compounds and reaction intermediates on the catalyst surface. The activity experiments were carried out to find out the possible reaction mechanism and furthermore the kinetic equation for NO reduction by propene.     

Lean-DeNOx titania based monolithic catalysts

The activity of titania based copper and platinum monolithic catalysts in the reduction of nitrogen oxides was studied with exhaust gases from a Diesel engine injecting fuel as reductant. Combining both catalysts, a two-stage system was designed, studying the influence of the copper catalysts composition on its performance with synthetic gas mixtures. The influence of reactants concentration and operating conditions was also investigated. Taking into account these results, a double-bed system with a cell density of 33 cell cm⁻² (210 c.p.s.i.) was prepared. Linear velocity had a strong influence on the performance of the Pt catalyst and of the double-bed. Two NO_x conversion maxima were observed with Pt/TiO₂ at 225°C and 350°C operating at 6.6 m s⁻¹. Promising NO_x conversions were achieved in the temperature range 200–450°C.     

Oxidation of potato starch with NO2: characterization of the carboxylic acid salts

Oxidation of primary hydroxyl groups of potato starch to the corresponding carboxylic acids was performed in a fluidized bed using N₂-diluted NO₂ as oxidant. FT-IR spectrum of the oxidized starch show the presence of two absorption bands at 1743 and 1379 cm⁻¹. The absorption at 1743 cm⁻¹ which normally attributed to carbonyl absorption vanishes after washing the oxidized starch by water. Then two new absorption bands appeared at 1650 and 1400 cm⁻¹ corresponding to the ionized carboxyl groups.

The presence of nitrate favor the un-ionized form of carboxyl groups and then the band at 1743 cm⁻¹ can be observed. Furthermore, the ionized carboxyl absorption (1600, 1400 cm⁻¹) are replaced by carbonyl absorption at 1743 cm⁻¹ by adding DCl. By means of ¹³C NMR analysis, oxidized starch, show a band around 200 ppm attributed to carboxylic acid, no formic acid was detected indicating that no cleavage took place under the applied reactions conditions.     

Performance of microchannel reactor combined with combustor for methanol steam reforming

The microchannel reactor with combustor for methanol steam reforming was fabricated to produce hydrogen for onboard proton exchange membrane (PEM) fuel cell device. A commercial copper-containing catalyst (Cu/ZnO/Al₂O₃) and Pt/ZrO₂ were used as a catalyst for methanol steam reforming and combustion reaction, respectively. It was found that catalyst layer with zirconia sol solution in microchannel showed no crack on the surface of catalyst layer and an excellent adherence to stainless steel microchannel even after reaction. The temperature of combustor could be controlled between 200 and 300 °C depending on the methanol feed rate. The hydrogen flow of 3.9 l h⁻¹ hydrogen was obtained with the reforming feed flow rate of 3.65 ml h⁻¹ at 270 °C.     

Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM5

Copper ion-exchanged zeolites ZSM5 with SiO₂:Al₂O₃ molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560–5400 h⁻¹). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO₂ formation in the gas phase.

A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO₂:Al₂O₃ ratio, enhances the conversion of NO. A vibrational band at 1631 cm⁻¹ is observed below the light-off temperature and interpreted as a bridged nitrato group bound to Cu²⁺–O–Cu²⁺ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrato groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N₂O₃, also binds in a bridge configuration to the same Cu²⁺–O–Cu²⁺ dimers.

A second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm⁻¹ probes isolated copper ions.

A third infrared band at 2130 cm⁻¹ confirms previous observations of -ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for adsorption are blocked by Cu²⁺ ion-exchange. The 2130 cm⁻¹ species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice.

Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers.

A high SiO₂:Al₂O₃ ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.     

In situ IR and pulse reaction studies on the active oxygen species over SrF2/Nd2O3 catalyst for oxidative coupling of methane

Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF₂/Nd₂O₃ catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C₂ hydrocarbons. IR band of superoxide species (O₂⁻) was detected on the O₂-preadsorbed SrF₂/Nd₂O₃. The substitution of ¹⁸O₂ isotope for ¹⁶O₂ caused the IR band of O₂⁻ at 1128 cm⁻¹ to shift to lower wavenumbers (1094 and 1062 cm⁻¹), consistent with the assignment of the spectra to the O₂⁻ species. A good correlation between the rate of disappearance of surface O₂⁻ and the rate of formation of gas phase C₂H₄ was observed upon interaction of CH₄ with O₂-preadsorbed catalyst at 700 °C. The O₂⁻ species was also observed on the catalyst under working condition. These results suggest that O₂⁻ species is the active oxygen species for OCM reaction on SrF₂/Nd₂O₃ catalyst.     

Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

Mn/MFI catalyzed reduction of NOx with alkanes

Mn/MFI catalysts were prepared by different methods and probed as catalysts for the catalytic reduction of NO_x with CH₄ or iso-butane in a gas flow containing excess O₂. Mn/MFI with high manganese loading was obtained by solid state ion exchange (SSI). The intensity of an IR band at 957 cm⁻¹, which is due to the perturbation of zeolite lattice vibrations by Mn ions attached to cage walls is proportional to the Mn content of the catalysts. Conversely, the intensity of the 3610 cm⁻¹ band, assigned to Brønsted acid sites decreases linearly with the Mn loading. A catalyst obtained by exchanging Na/MFI with an aqueous solution of Mn acetate is found most active for NO_x reduction with methane. Transport by surface diffusion of Mn ions from MnI₂ to exchange positions in MFI is more efficient than their transport through the gas phase. High NO conversion over proton-free catalysts indicates that protons are not instrumental in NO_x reduction over Mn/MFI.     

Thermodynamic studies on hydrogen adsorption on the zeolites Na-ZSM-5 and K-ZSM-5

Adsorption of dihydrogen onto the zeolites Na-ZSM-5 and K-ZSM-5 renders the fundamental H–H stretching mode infrared active. The corresponding infrared absorption bands were found at 4101 and 4112 cm⁻¹ for H₂/Na-ZSM-5 and H₂/K-ZSM-5, respectively. Thermodynamic characterization of the adsorbed state was carried out by means of variable-temperature infrared spectroscopy; simultaneously measuring integrated band intensity, temperature and equilibrium pressure of the gas phase. For the H₂/Na-ZSM-5 system, the standard adsorption enthalpy and entropy resulted to be ΔH° = −10.3 (±0.5) kJ mol⁻¹ and ΔS° = −121 (±10) J mol⁻¹ K⁻¹. For H₂/K-ZSM-5 corresponding values were −9.1 (±0.5) kJ mol⁻¹ and −124 (±10) J mol⁻¹ K⁻¹, respectively.     

CNG engines exhaust gas treatment via Pd-Spinel-type-oxide catalysts

Four spinel-type catalysts AB₂O₄ (CoCr₂O₄, MnCr₂O₄, MgFe₂O₄ and CoFe₂O₄) were prepared and characterized by XRD, BET, TEM and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a temperature-programmed combustion (TPC) apparatus. Spinel-type-oxides containing Cr at the B site were found to provide the best results. The half-conversion temperature of methane over the CoCr₂O₄ catalyst was 376 °C with a W/F = 0.12 g s/cm⁻³. On the basis of temperature-programmed oxygen desorption (TPD) analysis as well as of catalytic combustion runs, the prevalent activity of the CoCr₂O₄ catalyst could be explained by its higher capability to deliver suprafacial, weakly chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of palladium deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and CoCr₂O₄ catalysts enables half methane conversion at 330 °C (GHSV = 10,000 h⁻¹), a performance similar to that of conventional 4 wt% Pd-γ-Al₂O₃ catalysts but enabled with just a four-fold lower amount of noble metal.     

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm⁻¹ were identified in the region of the CH overtones (5200–6200 cm⁻¹). Among them, two bands at 5810 (aliphatic) and 6010 cm⁻¹ (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm⁻¹), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm⁻¹ (free-end) can be observed.     

The catalytic activity and methanol tolerance of transition metal modified-ruthenium–selenium catalysts

The activity of ruthenium-based catalysts towards oxygen reduction was enhanced by addition of tungsten, molybdenum and rhodium. The catalysts were produced by decarbonylation of the ruthenium and transition metal carbonyls in the presence of selenium (sulphur) and carbon powders. The produced materials were characterised by scanning electron microscopy and energy dispersive spectroscopy as well as by electrochemical evaluations in both half cells and direct methanol fuel cells. All transition metal-modified catalysts exhibited better performance than those of ruthenium–selenium (sulphur) alone, but the tungsten modification seemed the best approach. The RuSe_0.20W_0.29 catalyst delivered the maximum power density of up to 40 mW cm⁻². The improvement is a consequence of the enhanced activity towards oxygen reduction with a minor loss in methanol tolerance as well as a stabilising effect of tungsten on catalysts. The new catalysts were compared to Pt and to sulphur-containing catalysts.     

The reactions of ethanol over M/CeO2 catalysts: Evidence of carbon–carbon bond dissociation at low temperatures over Rh/CeO2

The reactions of ethanol over Rh/CeO₂ have been investigated using the techniques of temperature programmed desorption (TPD) and FT-IR spectroscopy, in addition to steady state catalytic tests. A comparison with previous studies of ethanol adsorption over Pd/CeO₂ [J. Catal. 186 (1999) 279] and Pt/CeO₂ [J. Catal. 191 (2000) 30] catalysts is presented. The apparent activation energy for the reaction was 49, 40, and 43 kJ mol⁻¹ for Rh/CeO₂, Pd/CeO₂ and Pt/CeO_2, respectively, while the turnover number (TON) at 400 K was 5.9, 8.6 and 2.6, respectively. Surface compositions of catalysts were characterised by XPS. A decrease of the atomic O(1s)/Ce(3d) ratio of the CeO₂ support indicates its partial reduction upon addition of the noble metal. The extent of reduction per metal atom was in the following order: Pt>Pd>Rh. FT-IR and TPD studies have shown that dehydrogenation of ethanol to acetaldehyde occurred over Pd/CeO₂, Pt/CeO₂ and Rh/CeO₂. Moreover, Rh/CeO₂ readily dissociated the C–C bond of ethanol at room temperature to form adsorbed CO (IR bands at 1904–2091 cm⁻¹). This was corroborated by the low desorption temperature of CH₄ over Rh/CeO₂ (450 K) when compared to that of Pd/CeO₂ (550 K) or Pt/CeO₂ (585 K).     

Effects of electrodeposited Co and Co–P catalysts on the hydrogen generation properties from hydrolysis of alkaline sodium borohydride solution

Co and Co–P catalysts electroplated on Cu in sulfate based solution without or with an addition of H₂PO₂⁻ ions were developed for hydrogen generation from alkaline NaBH₄ solution. The microstructures of the Co and Co–P catalysts and their hydrogen generation properties were analyzed as a function of cathodic current density and plating time during the electrodeposition. An amorphous Co–P electrodeposit with micro-cracks was formed by electroplating in the sulfate based solution containing H₂PO₂⁻ ions. It was found that the amorphous Co–P catalyst formed at 0.01 A/cm² exhibited 18 times higher catalytic activity for hydrolysis of NaBH₄ than did the polycrystalline Co catalyst. The catalytic activity of the electrodeposited Co–P catalyst for hydrolysis of NaBH₄ was found to be a function of both cathodic current density and plating time, that is, parameters determining the concentration of P in the Co–P catalyst. Especially, Co–13 at.% P catalyst electroplated on Cu in the Co–P bath at a cathodic current density of 0.01 A/cm² for 1080 s showed the best hydrogen generation rate of 954 ml/min g-catalyst in 1 wt.% NaOH + 10 wt.% NaBH₄ solution at 30 °C.     

Analysis of Fe species in zeolites by UV–VIS–NIR, IR spectra and voltammetry. Effect of preparation, Fe loading and zeolite type

Three procedures were employed for the preparation of Fe-zeolites with ZSM-5 (MFI), ferrierite (FER) and beta (BEA) structures: ion exchange from FeCl₃ solution in acetyl acetonate and solid-state ion exchange from FeCl₂ using an oxygen or nitrogen stream. A combination of UV–VIS–NIR spectra, IR spectra of skeletal vibrations and of adsorbed NO, as well as voltammetry provided information on the type of Fe species introduced. Single Fe(III) ion complexes (Fe(H₂O)_6−xOH_x) in hydrated zeolites were reflected in the charge-transfer bands at 33 100, 37 300 and 45 600 cm⁻¹. The single Fe(II) ions at cationic sites in evacuated zeolites yielded (through perturbation of framework T–O bonds) characteristic bands (910–950 cm⁻¹) in the region of the skeletal window. These Fe(II) ions with adsorbed NO were also reflected in vibrations at 1880 cm⁻¹. Dinuclear Fe–oxo complexes yielded the Vis band at 28 200 cm⁻¹. Voltammetry indicated the presence of Fe oxides (hematite) through the reduction peak at −0.7 V. Such oxide-like species were also reflected in the absorption edge at 19 800 cm⁻¹, and a doublet at 11 000 and 11 800 cm⁻¹ in the Vis spectra. Fe(II)–NO vibrations at 1840, 1810 and 1760 cm⁻¹ belonged to the undefined exposed Fe cations, probably originating from supported oxides. Using an ion exchange procedure, employing FeCl₃ in acetyl acetonate, exclusively Fe ions at cationic sites could be introduced at low concentrations (Fe/Al < 0.1). At higher Fe loadings, dinuclear Fe–oxo complexes were formed preferably in Fe-ZSM-5, but were absent in Fe-beta. Exclusively single Fe species could not be prepared at Fe concentrations above Fe/Al > 0.2; all three types of Fe species, single Fe ions, dinuclear Fe–oxo complexes and Fe oxides were formed.     

Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells

In this communication we discuss the properties of tungsten carbide, WC, as anodic electrocatalyst for microbial fuel cell application. The electrocatalytic activity of tungsten carbide is evaluated in the light of its preparation procedure, its structural properties as well as the pH and the composition of the anolyte solution and the catalyst load. The activity of the noble-metal-free electrocatalyst towards the oxidation of several common microbial fermentation products (hydrogen, formate, lactate, ethanol) is studied for microbial fuel cell conditions (e.g., pH 5, room temperature and ambient pressure). Current densities of up to 8.8 mA cm⁻² are achieved for hydrogen (hydrogen saturated electrolyte solution), and up to 2 mA cm⁻² for formate and lactate, respectively. No activity was observed for ethanol electrooxidation.

The electrocatalytic activity and chemical stability of tungsten carbide is excellent in acidic to pH neutral potassium chloride electrolyte solutions, whereas higher phosphate concentrations at neutral pH support an oxidative degradation.     

Hydrolytic decomposition of CF4 over alumina-based binary metal oxide catalysts: high catalytic activity of gallia-alumina catalyst

The hydrolytic decomposition of CF₄ has been conducted on gallia promoted alumina (Ga-Al oxide) catalysts at 803–903 K and 0.1 MPa. Steady state activity on 20% Ga-Al oxide was 15 times of that on Ce10%-AlPO₄ catalyst, on which the highest activity has been reported. The catalytic activity was further improved by incorporation of sulfate anion in Ga-Al oxide and by applying sol–gel method in preparation of the catalyst. XRD spectra of Ga-Al oxides showed a shift of diffraction peaks assigned to γ-alumina toward lower angles, indicating the formation of gallia-alumina solid solution. In situ FT-IR of pyridine adsorption spectra of Ga-Al oxides showed peaks solely attributable to Lewis acid (L-acid) sites at 1445–1455, ca. 1495, 1577, ca. 1594, and ca. 1622 cm⁻¹. The steady state catalytic activities increased with increasing peak areas at 1446 or 1622 cm⁻¹ of Ga-Al oxides with various Ga%, suggesting participation of Lewis acid sites into the reaction. It is demonstrate from surface area measurements of Ga-Al oxide catalyst before and after the reaction that not only higher catalytic activity but also higher catalyst stability were observed on Ga-Al oxide, Ga-Al oxide with sulfate, and Ga-Al oxide prepared by sol–gel method than on their parent oxides of alumina, Ga-Al oxide, and Ga-Al oxide prepared by incipient wetness method, respectively.     

The interaction of NO with Co/Co redox centres in CoAPOs catalysts: FTIR and UV–VIS investigations

The interaction of NO with Co²⁺/Co³⁺ redox sites in CoAPO-18 and CoAPO-5 catalysts was studied by means of FTIR and diffuse reflectance UV–Vis spectroscopy both at 298 and 85 K. Two families of Co²⁺ sites were found in the CoAPO-18 structure. (A) Ions in framework [Co²⁺(OH)P], associated with Brønsted acid sites which adsorb NO to produce dinitrosyls absorbing at 1903 and 1834 cm⁻¹; these dinitrosyl complexes are reactive, in that Co²⁺ is oxidized to Co³⁺ and N₂O is formed. (B) Structural defects Co²⁺ (Lewis acid sites) which stabilize dinitrosyls absorbing at 1900 and 1813 cm⁻¹. The NO adsorption both on reduced and, more significantly, on oxidised CoAPO-18 also leads to the formation of NO₂^δ+ adsorbed species. It was found that the two kinds of dinitrosyl complexes have different reactivity in presence of oxygen. Both families of sites are also present in CoAPO-5 catalysts on which, however, the redox reaction upon NO adsorption does not occur significantly.