Gas phase reaction of formaldehyde and hydrogen chloride in the presence of zeolite Y

The hydrogen and metal alkali forms of Y zeolite were tested in chlorination of CH₂O with HCl. It has been found that over alkali metal and hydrogen forms the only chlorinated product was methyl chloride, whereas in the presence of NH₄Y zeolite both methyl and methylene chlorides were formed. The conversion pathway of CH₂O itself seems to play an important role in the chlorination reaction mechanism. Methanol or methoxy species and dimethoxymethane are suggested as possible intermediates in the formation of CH₃Cl and CH₂Cl₂.     

Siloxanes with 1-oxypyridin-3-yl groups. Part 6. synthesis of copolymers and application as transacylation catalysts

Linear end-blocked and crosslinked siloxane copolymers containing dimethylsiloxyl and methyl(1-oxypyridin-3-yl)siloxyl groups were prepared and characterized thermally (TGA) and spectroscopically. These hydrophobic copolymers were found to be highly effective transacylation catalysts in the synthesis of carboxylic anhydrides and the hydrolysis of diphenyl phosphoro-chloridate (DPPC) under phase-transfer catalysis (PTC) conditions, i.e. CH₂Cl₂-H₂O suspension. The insolubility of the copolymers in water and the preference of the intermediate, polymeric 1-acyloxypyridinium ion for the more lipophilic carboxylate ion in anhydride formation suggest that the reaction occurs at the CH₂Cl₂-H₂O interphase. The rapid rate of hydrolysis of DPPC under PTC conditions and in water provides evidence for initial hydrophobic binding or association of the hydrophobic catalyst prior to reaction with a water-insoluble substrate.     

Electrosynthesis in systems of two immiscible liquids and a phase transfer catalyst. VII. The chlorination of substituted naphthalenes

The chlorination of 12 substituted naphthalenes by electrochemical oxidation in CH₂Cl₂/H₂O emulsions containing a phase transfer reagent, Bu₄N⁺, is described. In all cases the major product can be a monochlorinated derivative, selectivity commonly 40–90%, but the efficiency and selectivity of the reactions depend on the nature and position of the substituent as well as the choice of electrolysis parameters. The anodic chlorination of naphthalenes has also been studied using cyclic voltammetry in CH₃CN and it is clear that the mechanism depends on the oxidation potential of the naphthalene.     

IR study of chlorination of alumina employing mixtures of gaseous chlorine and carbon monoxide

The chlorination of an alumina with BET surface area of 100 m²/g has been studied in situ by transmission IR measurements at about 670 K. The chlorinating gases consisting of Cl₂ and CO were employed individually and in equimolar proportion. The IR results do not reveal the presence of a phosgene surface species which could support the only mechanism proposed so far to explain the chlorination. A detailed alternative reaction mechanism is suggested for the high temperature chlorination reaction, taking into account the IR results, together with the known electron donor-acceptor properties of the activated alumina and the reaction gases: Cl₂ molecules accept electrons from oxide ions with a lower coordination number on the alumina surface, leading to the formation of Cl^?and O_ad. While Cl^? yields AlCl₃, O_ad reacts further with CO producing CO₂.     

Chlorination of low-molecular-weight Euphorbia lactiflua natural rubber

The chlorination of low-molecular-weight natural rubber isolated from Euphorbia lactiflua latex (LMWER) was accomplished. The reaction was performed by using Cl_2(g), and CH₂Cl₂ or CCl₄ solvents. Different temperatures, reaction times and Cl₂ to isoprene ratio were used. The products were characterized by elementary analysis, infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The maximum chlorination reached was 59.9%. The properties were found to be comparable with chlorinated rubber obtained from liquid natural rubber (LNR). Received: 13 June 1997/Revised: 15 September 1997/Accepted: 23 September 1997     

Acid catalytic effects in the chlorination of propanoic acid

Selective α‐chlorination of propanoic acid to form 2‐monochloropropanoic (MCA) and 2,2‐dichloropropanoic acid (DCA) was investigated in a laboratory‐scale, semibatch reactor at 90–130 °C at atmospheric total pressure and in the presence of chlorosulfonic acid (ClSO₃H) and 2,2‐dichloroethanoic acid (DCA′) as catalytic agents and oxygen as a radical scavenger. The decomposition of the catalyst was investigated with sulfur analysis and UV‐spectrometry. The studies revealed that the majority of sulfur remains in the reaction mixture, but is converted to an inactive form during the chlorination. The reasons may be the decomposition of ClSO₃H and its reaction with propanoic acid. The kinetic experiments revealed autocatalytic and parallel formation of MCA and DCA, the selectivity being independent of Cl₂ concentration in the liquid phase. The experiments with DCA′ also demonstrated that DCA′ has a catalytic effect on the chlorination The experiments confirmed the validity of a previously proposed reaction scheme for α‐chlorination, which comprises the formation of the reaction intermediate (propanoyl chloride) from propanoic acid and ClSO₃H, the acid‐catalyzed enolization of the acid and a hydroxyl‐chlorine exchange reaction. The acid‐catalyzed enolization is the rate determining step in the reaction sequence. The kinetic data were fitted to rate equations based on the reaction scheme. © 2000 Society of Chemical Industry     

Structure and the catalysis mechanism of oxidative chlorination in nanostructural layers of a surface of alumina

On the basis of X-ray diffraction and mass spectrometric analysis of carrier γ-Al₂O₃ and catalysts CuCl₂/CuCl on its surface, the chemical structure of the active centers of two types oxidative chlorination catalysts applied and permeated type of industrial brands “Harshow” and “MEDС-B” was investigated. On the basis of quantum-mechanical theory of the crystal, field complexes were detected by the presence of CuCl₂ cation stoichiometry and structure of the proposed model crystal quasichemical industrial catalyst permeated type MEDС-B for oxidative chlorination of ethylene. On the basis of quantum-mechanical calculations, we propose a new mechanism of catalysis crystal quasichemical oxidative chlorination of ethylene reaction for the catalysts of this type (MEDС-B) and confirmed the possibility of such a mechanism after the analysis of mass spectrometric studies of the active phase (H₂ [CuCl₄]) catalyst oxidative chlorination of ethylene. The possibility of the formation of atomic and molecular chlorine on the oxidative chlorination of ethylene catalyst surface during Deacon reaction was displaying, which may react with ethylene to produce 1,2-dichloroethane. For the active phase (H [CuCl₂]), catalyst offered another model of the metal complex catalyst oxidative chlorination of ethylene deposited type (firm ‘Harshow,’ USA) and the mechanism of catalysis of oxidative chlorination of ethylene with this catalyst.     

Reforming of Methane with Carbon Dioxide over a Catalyst Consisting of Ruthenium Metal and Cerium Oxide Supported on Mordenite

Reforming of CH₄ with CO₂ proceeds at 400 °C over a catalyst consisting of ruthenium metal and CeO₂ highly dispersed on mordenite. The catalyst, Ru-CeO₂/MZ, is highly active for the reforming of CH₄ under the conditions at which a carbon formation reaction is thermodynamically apt to take place. The reforming selectively forms H₂ and CO. An increase in the weight of the catalyst resulting from carbon deposits was scarcely observed. IR spectra for the catalyst indicate that the reforming proceeds via the formation of the intermediate species such as Ru-CO and Ru-CH_x on the surface of ruthenium. The data of H₂ adsorption support the idea that ruthenium is highly dispersed in Ru-CeO₂/MZ.     

Influence of chlorine poisoning of copper/alumina catalyst on the selective hydrogenation of crotonaldehyde

The effect of the presence of chlorine on the activity and selectivity of a Cu/Al₂O₃ catalyst has been examined for the selective hydrogenation of an unsaturated aldehyde, crotonaldehyde. Cu/Al₂O₃ in the absence of chlorine poisons produced 1-butanol almost exclusively, whereas catalysts pre-dosed with a suitable amount of chlorine compound (CCl₄, CHCl₃ and CH₂Cl₂) shifted the product distribution towards formation of butanal. The poisoning effectiveness increased in the order CCl₄32Cl₂CH₃Cl and methyl chloride was found to totally deactivate the catalyst. The most significant enhancement in butanal selectivity was observed with CCl₄ and CH₂Cl₂. The effect of chlorine as a poison is in contrast to the effect of sulphur which enhances formation of crotyl alcohol and the origins of these effects are discussed.     

The role of Cl− in a Li+-ZnO-Cl− catalyst on the oxidative coupling of methane and the oxidative dehydrogenation of ethane

The effect of Cl^? ion addition to a Li⁺-ZnO catalyst has been studied with respect to the oxidative coupling of CH₄ and the oxidative dehydrogenation (OXD) of C₂H₆. Increasing the Cl/Li ratio from 0.65 to 0.90 had relatively little effect on the CH₄ conversion, whereas the C₂H₄/C₂H₆ ratio was enhanced significantly as a result of an increase in the OXD reaction rate. Conversely, loss of Cl^? from the catalyst during the reaction had a much more deleterious effect on ethane OXD activity than on methane coupling activity. Addition of Cl^? ions at a Cl/Li ratio of 0.9 caused a decrease both in the number of basic sites and in the basic strength of these sites, as determined by temperature-programmed desorption of CO₂. The similarities between the results obtained over Li⁺-ZnO-Cl^? catalysts and those previously reported for Li⁺-MgO-Cl^? catalysts confirm that basicity of the host oxide plays only a minor role in determining the properties of these chlorided catalysts.     

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.     

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.     

Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported group VIII metal catalysts

Mechanisms of partial oxidation of methane to synthesis gas were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing 1 and 3 ml pulses of a mixture of CH₄ and O₂ (2/1). With Ir, Pt and Ni/TiO₂ catalysts, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse. The synthesis gas production basically proceeded via two-step paths consisting of highly exothermic complete methane oxidation to give H₂O and CO₂, followed by the endothermic reforming of methane with H₂O and CO₂. In contrast, with the Rh and Pd/TiO₂ catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH₄/O₂ (2/1) pulse and a small increase in the temperature at the rear end was observed. Initially, the endothermic decomposition of CH₄ to H₂ and deposited carbon or CH_x probably took place at the front edge of the catalyst bed, after which the deposited carbon or generated CH_x species would be oxidized into CO_x. When the Ru/TiO₂ catalyst was used, a temperature increase at the front edge of the catalyst bed was observed upon introduction of the 3 ml pulse of CH₄/O₂. In contrast, the temperature drop at the front edge of the catalyst bed was observed for a 1 ml pulse of CH₄/O₂. These results seemed to exhibit two possibilities for a synthesis gas formation route over the Ru/TiO₂ catalyst. The reaction pathway of the partial oxidation of methane with group VIII metal-loaded catalysts depended strongly upon the metal species and reaction conditions.     

A Comparison of Oxygen-vacancy Effect on Activity Behaviors of Carbon Dioxide and Steam Reforming of Methane over Supported Nickel Catalysts

Partial oxidative steaming reforming of methanol (POSRM) to produce hydrogen selectively for polymer electrolyte membrane fuel cell (PEMFC) powering vehicles was studied over Cu–ZnO/samaria-doped ceria (SDC) catalyst. Compared with Cu–ZnO/α-Al₂O₃ and Cu–ZnO/γ-Al₂O₃ catalysts, the Cu–ZnO/SDC catalyst exhibited higher activity for CH₃OH conversion and higher selectivity for H₂ production in the POSRM reaction. The higher catalytic performance of Cu–ZnO/SDC appears attributable to the support effect of SDC. Effects of reaction temperature, O₂/CH₃OH and H₂O/CH₃OH molar ratios on the catalytic performance of Cu–ZnO/SDC were investigated. It has been found that the partial-oxidation nature of the POSRM reaction is increased when O₂/CH₃OH ratio is increased, and the combustion of methanol and H₂ would occur insignificantly in the POSRM over the Cu–ZnO/SDC catalyst. A higher concentration of steam is beneficial to suppress CO formation over the Cu–ZnO/SDC catalyst. Under the experimental conditions of the present work, the O₂/CH₃OH and H₂O/CH₃OH molar ratios should be about 0.02 and 1.0–2.0, respectively, in order for Cu–ZnO/SDC to achieve an optimum catalytic performance.     

Catalyst Structure-Performance Relationship Identified by High-Throughput Operando Method: New Insight for Silica-Supported Vanadium Oxide for Methanol Oxidation

The reaction mechanism of methanol oxidation catalyzed by vanadium oxides on a silica support (V₂O₅/SiO₂) was investigated in a high-throughput operando reactor coupled with a Fourier transform-infrared (FT-IR) imaging system for rapid product analysis and six parallel, in situ Raman spectroscopy probes for catalyst characterization. Up to six V₂O₅/SiO₂ catalysts with different vanadium loadings (i.e., from 0 to 7%) were simultaneously monitored under identical experimental conditions. The specific Raman bands of the different catalysts in the six parallel reaction channels are quantitatively determined in this work. Under steady-state reaction conditions, the Raman intensities of C–H stretch in Si–O–CH₃ and V–O–CH₃ were extensively studied at different reaction temperatures and different vanadium loadings. For the first time, we observed enhanced Si–O–CH₃ formation on V₂O₅/SiO₂ catalysts with low vanadium loadings. We attribute this phenomenon to surface cluster edge activation. Careful comparison of the in situ Raman intensity of V–O–CH₃ on V₂O₅/SiO₂ catalysts revealed different methoxy formation mechanisms in different reaction temperature regimes.     

Adsorption and Reactions of CH2I2 on Clean and Oxygen-Modified Ag(111): a RAIRS and TPD Study

The surface chemistry of CH₂I₂ on Ag(111) in the presence and absence of pre-adsorbed O, produced by NO₂ adsorption at elevated temperature, has been examined using temperature-programmed desorption and reflection absorption infrared spectroscopy. There is good evidence for the formation of adsorbed methylene, CH₂(a), that reacts with another CH₂(a) to form and desorb ethylene, C₂H₄(g), in a reaction-limited process. Increasing the surface coverage of CH₂I₂ hinders both the dissociation and recombination processes indicated by the upward temperature shift in the formation of C₂H₄. Co-adsorbed O atoms strengthen the bonding of CH₂I₂ to the surface; the increased thermal stability is up to 60 K. The formation of C₂H₄ decreases with increasing amounts of pre-adsorbed O; the main reaction product is CH₂O produced in a reaction-limited process. CH₂O forms either on the chemisorbed or on the oxide phase with desorption peak temperatures of 225 and 270 K, respectively. The formation of gas-phase carbon dioxide suggests that a formate intermediate is involved in a secondary reaction pathway.     

Mechanistic Study of Selective Oxidation of Dimethyl Ether to Formaldehyde over Alumina-supported Molybdenum Oxide Catalyst

XPS and IR spectroscopies were used to investigate the surface intermediates of dimethyl ether (DME) oxidation to formaldehyde over MoOx/Al₂O₃ catalyst. The reaction performances were tested by employing three typical reaction conditions, depending on the O₂/DME ratio and the reaction temperature. When there was sufficient oxygen present in the reaction media, a terminal or bridged CH₃O* species formed by DME dissociation was highly active and rapidly reacted with lattice oxygen to produce formaldehyde, leading to higher selectivity of HCHO. When oxygen was consumed completely or only DME was present in the reaction media, CH₃O species bonded to more than two Mo atoms (μ-OCH₃) and CH_x (x=1–3) species attached to the Mo atoms were observed and the relative ratio of (μ-OCH₃) /Mo–CH_x was significantly dependent on the reduction degree of MoO_x domains. The (μCH₃O) species was related to the formation of CH₃OH or CO_x, and the Mo–CH_x species led to the formation of CH₄.     

Novel synthesis of phosphorus containing polymers under inverse phase transfer catalysis

A novel synthesis of polyphosphates by inverse phase transfer catalysis (IPTC) was investigated. The reaction of methylphosphoric dichloride (MPD) and sodium salt of bisphenol A (BA) in two-phase H₂O/CH₂Cl₂ medium under IPTC is presented and the results are evaluated by the yield and inherent viscosity values. The biphasic medium does not require rigorous stirring. The polyphosphate was characterized by IR, ¹H NMR, ³¹P NMR, inherent viscosity, thermal analysis, and molar mass. Pyridine (Py), pyridine-oxide (PNO) and 4-dimethylamino-pyridine (DMAP) were used as the inverse phase transfer catalysts. DMAP was found to be the best catalyst.     

Synthesis,characterization and catalytic study of a novel iron(III)-tridentate Schiff base complex in sulfide oxidation by UHP

An hydrazone Schiff base-iron(III) complex using salicylidene benzoyl hydrazine (L) as ligand has been synthesized and characterized by elemental analyses, IR, ¹H and ¹³C NMR and UV–Vis spectroscopy. Oxidation of sulfides to sulfoxides in one-step was conducted by this complex catalyst using urea hydrogen peroxide (UHP) in mixture of CH₂Cl₂/CH₃OH (1:1) under air at room temperature. The effect of the reaction conditions on the oxidation of methylphenylsulfide was studied by varying the amount of the catalyst, reaction temperature, reaction time and the amount of UHP. The results showed that using this system in the oxidation of sulfides, sulfoxides were obtained as the main products, together with variable amounts of sulfones (?9%), depending on the nature of the substrate.     

A cis-directing effect towards diols by an exocyclic P-NHR moiety in cyclotriphosphazenes

Cyclophosphazenes containing the P-NHR moiety in an exocyclic spiro ring, N₃P₃Cl₄[NH(CH₂)₃O], (1), and N₃P₃Cl₄[NH(CH₂)₃NMe], (2), were used to investigate a possible directing effect of the P-NHR moiety on the formation of products in the nucleophilic substitution reactions with diols such as tetraethyleneglycol, 1,3-propanediol and 2,2-dimethyl-1,3-propanediol. The ³¹P NMR spectra of the reaction mixtures showed that only one kind of ansa product is formed in each of these reactions. X-ray crystallographic studies of the ansa products [(4a), (5a), (6a) and (7a)] have provided definitive proof of the cis-directing effect of the P-NHR moiety in cyclotriphosphazenes. It is likely that hydrogen-bond interaction between the incoming nucleophile and the P-NHR moiety of the reactant accounts for the preference for products with the substituents cis to the NH group.