Evolution of Ti–Sn-rutile-supported V2O5–WO3 catalyst during its use in nitric oxide reduction by ammonia

This paper concerns the relation between surface structure of crystalline vanadia-like active species on vanadia–tungsta catalyst and their activity in the selective reduction of NO by ammonia to nitrogen. The investigations were performed for Ti–Sn-rutile-supported isopropoxy-derived catalyst. The SCR activity and surface species structure were determined for the freshly prepared catalyst, for the catalyst previously used in NO reduction by ammonia (320 ppm NO, 335 ppm NH₃ and 2.35 vol% O₂) at 573 K as well as for the catalyst previously annealed at 573 K in helium stream containing 2.35 vol% O₂. The crystalline islands, exposing main V₂O₅ surface, with some tungsten atoms substituted for V-ones, were found, with XPS and FT Raman spectroscopy, to be present at the surface of the freshly prepared catalyst. A profound evolution of the active species during the catalyst use at 573 K was observed. Dissociative water adsorption on V⁵⁺OW⁶⁺ sites is discussed as mainly responsible for the catalyst activity at 473 K and that on both V⁵⁺OW⁶⁺ and V⁴⁺OW⁶⁺ sites as determining the activity at 523 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimizing the catalyst circulation ratio in a reformer with a moving bed via a combination of real and computational experiments

During the operation of continuous catalyst regeneration reformers, the problem of optimizing the catalyst circulation ratio in the reactor-regenerator system arises. This problem is solved by a combination of real and computational experiments to investigate the regularities of coking on a catalyst’s surface. Based on TGA results for industrial Pt-Sn/γ-Al₂O₃ catalyst, it is concluded that amorphous coke is formed on the catalyst’s surface during reforming, its quantity at the reactor block outlet being 4–6%, depending on the feed composition and technological parameters of the process. The specific surface of samples is 152 m²/g for the fresh catalyst, 140 m²/g after regeneration, and 118 m²/g at the reactor outlet, which correlates with the quantity of coke on the surface of samples. Mathematical analysis of the coking processes in a reformer with a moving bed show that the catalyst circulation ratio must be maintained in the range of 0.008–0.010 m³/m³ to increase the operating efficiency of an industrial unit. Maintaining optimal conditions enables us to control the coking process, keeping coke concentration as low as possible and the catalyst specific surface as high as possible.     

A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe

20%SrO-20%La₂O₃/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH₄ conversion and 80% C₂-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH₄O₂ molar ratio=91 and total flow rate of 100 ml/min. Addition of SrO onto La₂O₃/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH₄ conversion and C₂-selectivity. Meanwhile, the reaction temperature required to obtain the highest C₂-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO₂ added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO₂ will suppress the formation of CO₂ produced via the OCM reaction, therefore, improves the C₂-selectivity. The FT-IR spectra of CO₂ adspecies recorded at different temperatures show that CO₂ interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO₂ adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca²⁺ cations at room temperature. If the temperature is higher than 473 K, it will form on La³⁺ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca²⁺ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr²⁺ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO₂-TPD. The role of the surface basicity of the SLC catalyst is also discussed.     

Characteristics of commercial selective catalytic reduction catalyst for the oxidation of gaseous elemental mercury with respect to reaction conditions

The performance of V₂O₅/TiO₂-based commercial SCR catalyst for the oxidation of gaseous elemental mercury (Hg⁰) with respect to reaction conditions was examined to understand the mechanism of Hg⁰ oxidation on SCR catalyst. It was observed that a much larger amount of Hg⁰ adsorbed on the catalyst surface under oxidation condition than under SCR condition. The activity of commercial SCR catalyst for Hg⁰ oxidation was negligible in the absence of HCl, regardless of reaction conditions. The presence of HCl in the reactant gases greatly increased the activity of SCR catalyst for the oxidation of Hg⁰ to oxidized mercury (Hg²⁺) such as HgCl₂ under oxidation condition. However, the effect of HCl on the oxidation of Hg⁰ was much less under SCR condition than oxidation condition. The activity for Hg⁰ oxidation increased with the decrease of NH₃/NO ratio under SCR condition. This might be attributed to the strong adsorption of NH₃ prohibiting the adsorption of HCl which was vital species promoting the oxidation of Hg⁰ on the catalyst surface under SCR condition.     

Oxidative Regeneration of Sulfide-fouled Catalysts for Water Treatment

This study tested the stability, activity, and selectivity of an alumina-supported Pd–In bimetallic catalyst during repetitive sulfide fouling and oxidative regeneration conditions. Nitrate reduction with hydrogen was used as the probe reaction in a continuous-flow packed-bed reactor to assess changes in the catalyst structure as a result of the fouling and regeneration processes. Partial regeneration of a severely sulfide-fouled Pd–In catalyst was achieved with a NaOCl/NaHCO₃ solution. However, the regenerated catalyst had a reduced activity for NO₃ ^? reduction and increased selectivity towards NH₃. Analysis of the catalyst bed after regeneration experiments using XPS, ICP-MS, and BET surface area revealed that bulk structural transformations of the Pd–In bimetallic catalyst occurred, as a result of preferential Pd dissolution near the column influent. The dissolved Pd showed limited mobility in the column, and was re-deposited on the catalyst, resulting in Pd enrichment on the catalyst surface and redistribution of Pd towards the end of the column. These changes along with residual sulfur content on the catalyst surface were likely responsible for the increased selectivity towards NH₃. These results indicate the importance of limiting the exposure of reduced sulfur species to Pd-based catalysts, especially when treating contaminants like NO₃ ^?, where product selectivity is a priority.     

Electrochemically Induced Oscillations of C2H4 Oxidation Over Thin Sputtered Rh Catalyst Films

The electrochemically promoted induction of self-sustained catalytic rate and potential oscillations during C₂H₄ oxidation was studied over sputtered Rh thin (40 nm catalyst films interfaced with ZrO₂ (8 mol% Y₂O₃). The reaction rate oscillates simultaneously with the catalyst potential, and always in the opposite direction. The electrochemically induced oscillatory rate is typically 60 times larger than the open-circuit catalytic rate and 1000 times larger than the electrochemical rate of O²⁻ supply to the catalyst. The phenomenon is completely reversible and only observed under anodic polarization where the rate oscillates between the values corresponding to metallic Rh and surface Rh₂O₃. The oscillations are caused by the electrochemically controlled backspillover of O²⁻ to the catalyst surface and the concomitant, via repulsive lateral interactions, decomposition of surface rhodium oxide followed by surface reoxidation to Rh₂O₃ by gaseous O₂.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

N2O Decomposition Catalysed by Transition Metal Ions

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al₂O₃), reduced nickel catalyst (Ni⁰/Al₂O₃), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al₂O₃) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH₄/O₂ reaction, even with a pre-reduced nickel catalyst, and Ni⁰ is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni⁰ is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

Selective Isopropylation of Biphenyl to 4,4′-DIPB over Mordenite (MOR) Type Zeolite Obtained from a Layered Sodium Silicate Magadiite

Molybdenum carbide catalysts for water–gas shift (WGS) reaction were investigated to develop an alternate commercial LTS (Cu-Zn/Al₂O₃) catalyst for an onboard gasoline fuel processor. The catalysts were prepared by a temperature-programmed method and were characterized by N₂ physisorption, CO chemisorption, XRD and XPS. It was found that the Mo₂C catalyst showed higher activity and stability than the commercial LTS catalyst, even though both catalysts were deactivated during the thermal cycling runs. The optimum carburization temperature for preparing Mo₂C was in the range of 640–650 °C. It was found that the deactivation of the Mo₂C catalyst was caused by the transition of Mo^δ+ (IV < δ⁺ < VI, MoO_xC_y), Mo^IV and Mo₂C on the surface of the Mo₂C catalyst to Mo^VI (MoO₃) with the reaction of H₂O in the reactant. It was identified that molybdenum carbide catalyst is an attractive candidate for the alternate Cu-Zn/Al₂O₃ catalyst for automotive applications.     

A REACTION-EXTRACTION-REGENERATION SYSTEM FOR HIGHLY SELECTIVE OXIDATION OF BENZENE TO PHENOL

The reaction-extraction-regeneration system for the liquid-phase oxidation of benzene to phenol in the benzene-water-oxygen system was investigated. Phenol was extracted in the extractor to reduce the concentration of phenol in the benzene phase. As vanadium catalyst was oxidized to inactive species after the oxidation reaction, the regenerator was installed in the system to reduce the oxidation state of vanadium catalyst from V⁴⁺ or VO²⁺ to the active V³⁺ under H₂ flow. The effects of various operating parameters including concentration of VCl₃ catalyst, O₂ and H₂ flow rates, benzene bubble size, pH, surface area of Pt regeneration catalyst, the metal species, and amount of ascorbic acid were investigated. Ascorbic acid was employed as a reducing agent for helping reduce the V⁴⁺ form to the active form and therefore improving the activity of vanadium catalyst. VCl₃ catalyst concentration of 10 mol/m³ with pH of 3–4 in the reactor and Pt surface area of 0.05 m² in the regenerator showed optimal conditions for the system.     

Porous MnO<Subscript>2</Subscript>/CNT catalysts with a large specific surface area for the decomposition of hydrogen peroxide

H₂O₂ vapor sterilization is an effective and safe method for removing various pathogens. To improve the efficiency of this technique, the time required for sterilization must be shortened. The aeration time constitutes a large portion of the total sterilization time; therefore, the development of a catalyst for H₂O₂ decomposition is necessary. Bulk MnO₂ is typically used in H₂O₂ decomposition, but it has a low specific surface area. To increase H₂O₂ decomposition activity, specific surface area and electron transfer ability of catalyst need improvement. In this study, MnO₂/CNT(x), where x denotes the weight ratio of CTAB to H₂O in the catalyst preparation, was synthesized using a soft template method with varying amounts of the template. Overall, the catalyst specific surface area remarkably increased to 190–200 m²/g from 0.043 m²/g for bulk MnO₂ and these increased surface areas resulted in superior H₂O₂ decomposition activity. Among the CNT-supported catalysts tested, MnO₂/CNT (1.0) exhibited the highest activity, which was 570 times that of bulk MnO₂. Aeration times were also calculated with some assumptions and the aeration can be finished within 1 hr (bulk MnO₂ needs about 25 hr).     

Effects of mercury oxidation on V2O5–WO3/TiO2 catalyst properties in NH3-SCR process

The effects of mercury oxidation on V₂O₅–WO₃/TiO₂ SCR catalyst's physical and chemical properties have been investigated. Both fresh catalyst and mercury exposed catalyst have been examined by BET, XRD, XPS and catalytic activity measurements. Mercury oxidation promoted the V^5 + species transforming to the V^4 + species and consumed the lattice oxygen on the surface of catalyst. In addition, the NO conversion of mercury exposed catalyst decreased in the range of 200 °C to 300 °C. It suggested a competitive relationship between gaseous NH₃ and adsorbed mercury on the catalyst surface in that temperature range.     

Effects of pore diameter and catalyst loading in hydroliquefaction of coal with CoO/MoO3/Al2O3 catalysts

The effect of catalyst pore size has been studied for the hydroliquefaction of a West Virginia coal in the presence of Co/Mo/Al₂O₃ catalyst. The alumina supports used for catalyst preparation had relatively sharp, unimodal pore size distribution with average pore diameters in the range of 100 Å to almost 1000 Å. Loading of MoO₃ and CoO on the Al₂O₃ supports was in the constant weight ratio of 5:1, but the absolute loading was in direct proportion to the surface area of the support. Two series of catalyst were studied: “High loading”, with 9.7 × 10^?4 g MoO₃/m² Al₂O₃, and “low loading”, with 4.5 × 10^?4 g MoO₃/m² Al₂O₃; both loadings were less than the amount necessary for monolayer distribution of MoO₃ on Al₂O₃. The weight of catalyst charged in each autoclave run was varied so that the same weight of MoO₃ and CoO was present for each experiment.The principal results were: (1) Al₂O₃ alone is not catalytic, even in large amount; (2) conversion of coal increases as catalyst pore diameter increases; from 100 Å to at least 500 Å; (3) the increased conversion with increasing pore size is manifested mainly as increased yield of asphaltenes at 400°C, so the ratio of oil to oil-plus-asphaltenes decreases as pore diameter increases; and (4) catalysts with “low loading” of MoO₃ and CoO on the Al₂O₃ surface give higher liquefactions than their counterparts with “high loading”. Most of the results are consistent with an expected low diffusion rate of large, coal-derived molecules through the catalyst pore system. The higher liquefaction with “low loading” of the Al₂O₃ surface might result from slow desorption of large product molecules (asphaltenes) exhibiting multiple-site adsorption to Mo neighbors on the surface.     

Removal of elemental mercury from simulated flue gas by cerium oxide modified attapulgite

A novel catalyst CeO₂/ATP was developed to remove Hg⁰ from coal fired gas. This is new way to use the facile, cheap and larger BET specific surface area catalyst attapulgite (ATP) as support to remove Hg⁰ from coal fired gas. The Hg⁰ removal and oxidation efficiency of CeO₂/ATP (1: 1) is up to 97.75% and 92.23% at 200 °C, respectively. We also found that ATP plays an important role in improving the catalyst activity of CeO₂/ATP, which can make CeO₂/ATP have more stable catalyst activity at broader temperature range and obtain lower optimum activity temperature. Other influencing factors, such as temperature and flue gas environment (SO₂, Cl₂, NO), are also investigated in order to get a clear understanding of the experiment. The formation mechanisms are also proposed.     

Porous versus novel compact Ziegler–Natta catalyst particles and their fragmentation during the early stages of bulk propylene polymerization

The effect of the porosity of Ziegler–Natta catalyst particles on early fragmentation, nascent polymer morphology, and activity were studied. The bulk polymerization of propylene was carried out with three different heterogeneous Ziegler–Natta catalysts under industrial conditions at low temperatures, that is, with a novel self‐supported catalyst (A), a SiO₂‐supported catalyst (B), and a MgCl₂‐supported catalyst (C), with triethyl aluminum as a cocatalyst and dicyclopentyl dimethoxy silane as an external donor. The compact catalyst A exhibited no measurable porosity and a very low surface area (<5 m²/g) by Brunauer–Emmet–Teller analysis, whereas catalysts B and C showed surface areas of 63 and 250 m²/g, respectively. The surface and cross‐sectional morphologies of the resulting polymer particles at different stages of particle growth were analyzed by scanning electron microscopy and transmission electron microscopy. The compact catalyst A showed homogeneous and instantaneous fragmentation already in the very early stages of polymerization, which is typically observed for porous MgCl₂‐supported Ziegler–Natta catalysts. Moreover, the compact catalyst particles gave rise to almost perfectly spherical polymer particles with a smooth surface. In contrast, the silica‐supported catalyst B gave rise to particles having a cauliflower morphology, and the second reference catalyst C produced fairly spherical polymer particles with a rough surface. All of the three catalysts exhibited similar activities of 450 g of polypropylene/g of catalyst after 30 min of polymerization, and most interestingly, the comparative kinetic data presented indicated that the reaction rates were not influenced by the porosity of the catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Investigating the Influence of Fe Speciation on N<Subscript>2</Subscript>O Decomposition Over Fe–ZSM-5 Catalysts

The influence of Fe speciation on the decomposition rates of N₂O over Fe–ZSM-5 catalysts prepared by Chemical Vapour Impregnation were investigated. Various weight loadings of Fe–ZSM-5 catalysts were prepared from the parent zeolite H-ZSM-5 with a Si:Al ratio of 23 or 30. The effect of Si:Al ratio and Fe weight loading was initially investigated before focussing on a single weight loading and the effects of acid washing on catalyst activity and iron speciation. UV/Vis spectroscopy, surface area analysis, XPS and ICP-OES of the acid washed catalysts indicated a reduction of ca. 60% of Fe loading when compared to the parent catalyst with a 0.4 wt% Fe loading. The TOF of N₂O decomposition at 600 °C improved to 3.99?×?10³ s^?1 over the acid washed catalyst which had a weight loading of 0.16%, in contrast, the parent catalyst had a TOF of 1.60?×?10³ s^?1. Propane was added to the gas stream to act as a reductant and remove any inhibiting oxygen species that remain on the surface of the catalyst. Comparison of catalysts with relatively high and low Fe loadings achieved comparable levels of N₂O decomposition when propane is present. When only N₂O is present, low metal loading Fe–ZSM-5 catalysts are not capable of achieving high conversions due to the low proximity of active framework Fe³⁺ ions and extra-framework ɑ-Fe species, which limits oxygen desorption. Acid washing extracts Fe from these active sites and deposits it on the surface of the catalyst as Fe_xO_y, leading to a drop in activity. The Fe species present in the catalyst were identified using UV/Vis spectroscopy and speculate on the active species. We consider high loadings of Fe do not lead to an active catalyst when propane is present due to the formation of Fe_xO_y nanoparticles and clusters during catalyst preparation. These are inactive species which lead to a decrease in overall efficiency of the Fe ions and consequentially a lower TOF.     

Experimental technique for kinetic study of hydrogenation of fatty acid methyl esters in vapor phase

A new approach to kinetic studies of fat hydrogenation is discussed. An experimental setup is described in detail. An example of reactor performance in hydrogenation of fatty acid methyl esters is given. aPresent address: AB Karlshamns Oljefabriker, S-292 00 Karlshamn, Sweden. Notation: c, outlet concentration, mol/m³ ; c_o, inlet concentration, mol/m³: c_b, concentration in bulk fluid, mol/m³ ; c_s concentration at catalyst surface, mol/m³ ; d,pore diameter, m; D_e, effective diffusivity, m²/s; E, activation energy of reaction, J/mol; h, heat transfer coefficient, J/m² s K; ΔH, heat of reaction, J/mol; k_c, mass transfer coefficient, m/s; p, partial pressure, Pa; p_o, saturated vapor pressure, Pa; qf, total flow to reactor, m³/s; q_rec, recycle flow, m³/s; R, observed reaction rate per unit particle volume, mol/s m³ ; R_g, gas constant, J/mol K; r, observed reaction rate per unit mass of catalyst, mol/kg s; r_p particle radius, m; T_b, temperature of gas in bulk flow, K; T_s, temperature of gas at catalyst surface, K;-v, molar volume, m³/mol; V, volume of catalyst bed, m³ ; W, catalyst mass, kg. Greek symbols: σ, surface tension, N/m; λ_e, effective thermal conductivity of catalyst particle, J/m s K.     

Structure and performance of a novel TiO2-phosphonate composite photocatalyst

An innovative SiO₂-PO₄³⁻-TiO₂ photocatalyst is presented which is able to bond TiO₂ to Raschig rings (RR). Evidence for the formation on the catalyst surface of PO stretching bands near 1200–1250 cm⁻¹ is presented by FTIR spectroscopy. The TiO₂ Degussa P25 on the catalyst surface (RR) was further characterized by high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction showing that the composite catalyst prepared at 500 °C does not alter the particle size or crystallographic composition of the TiO₂ Degussa P25 particles. The Ti- and P-distribution of the catalyst surface overlayers was obtained by Ar-sputtering eroding up to 100 topmost catalyst layers. By atomic force microscopy (AFM) the root mean square roughness (Rq) or rugosity of 771 nm and an average height of the catalyst layer of 1.52 μm were found on the glass surface. The root mean square roughness Rq varies very little in value before and after the photocatalysis indicating that the sample porosity is conserved during 4-CP photodegradation. The disappearance kinetics of 4-chlorophenol (4-CP) on the SiO₂-PO₄³⁻-TiO₂ composite occurred within 15 min and was faster than the 45 min needed with suspensions of TiO₂ Degussa P25 (1 g L⁻¹). The SiO₂-PO₄³⁻-TiO₂ photocatalyst was able to degrade repetitively 4-CP solutions without loss of activity. The effect of the light intensity, oxidant concentration and 4-CP concentration on the photodegradation kinetics was investigated and is reported in this study.