Catalyzed Decomposition Reaction Research Articles

Photocatalytic properties of TiO2@polymer and TiO2@carbon aerogel composites prepared by atomic layer deposition

Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2. Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye.

A molecular electron density theory study of the Lewis acid–catalyzed decomposition reaction of nitroethyl benzoate using aluminum derivatives

AbstractThe molecular mechanism of the decomposition reaction of nitroethyl benzoate (NEB‐1) catalyzed by Lewis acids (LAs) based on aluminum metal, AlMe3, and AlCl3, in N,N‐dimethylacetamide, has been analyzed within the molecular electron density theory (MEDT) using calculations at the B3LYP(PCM)/6‐31+G(d) computational level. These LA‐catalyzed decomposition reactions take place via a two‐step mechanism involving a zwitterionic intermediate. The use of a more acidic AlCl3 LA favors the decomposition reaction, both kinetically and thermodynamically. The bonding evolution theory (BET) analyses indicate that these LA‐catalyzed decomposition reactions begin with the proton transfer process, followed by the extrusion of benzoic acid at the second step of the reaction.

Kinetics of Nano Titanium Dioxide Catalyzed Thermal Decomposition of Ammonium Nitrate and Ammonium Nitrate‐Based Composite Solid Propellant

AbstractThis study deals with the influence of nanosized titanium dioxide (TiO2) catalysts on the decomposition kinetics of ammonium nitrate (AN) and ammonium nitrate‐based composite solid propellant. TiO2 nanocatalyst with an average particle size of 10 nm was synthesized by sol‐gel method using titanium alkoxide as precursor. Formation of nanostructured TiO2 and presence of its anatase and brookite phases was confirmed by powder X‐ray diffraction (PXRD) and selected area diffraction (SAED) studies. Nano TiO2 was further characterized by transmission electron microscopy (TEM), infrared (IR) spectroscopy, and thermogravimetry. The catalytic effect of TiO2 nanocatalysts on the solid state thermal decomposition reaction of AN and nonaluminized HTPB/AN propellant was evaluated. To ascertain the effectiveness of the TiO2 nanocatalyst, the thermal kinetic constants for the catalytic and non‐catalytic decomposition of AN and AN propellant samples were computed by using a nonlinear integral isoconversional method. Catalytic influence was evident from the lowering of activation energy for the catalyzed decomposition reactions. Apparently, the nanocatalysts provide Lewis acid and/or active metal sites, facilitating the removal of AN dissociation products NH3 and HNO3 and thereby enhance the rate of decomposition. The changes in the critical temperature of thermal explosion of AN and AN propellant samples due to the addition of TiO2 nanocatalyst were also computed and the possible reasons for the changes are discussed.

Effect of anatase–brookite mixed phase titanium dioxide nanoparticles on the high temperature decomposition kinetics of ammonium perchlorate

In the present study, titanium dioxide (TiO2) nanocatalyst was synthesized using a titanium alkoxide precursor. The nanocatalyst was found to consist of anatase and brookite phases, with an average particle size of ∼10 nm. Formation of the nanostructured anatase–brookite mixed phase TiO2 was confirmed by powder XRD and SAED studies. The nanocatalyst was further characterized by TEM, FTIR and thermogravimetry. Catalytic effect of the TiO2 nanocatalyst on the solid state thermal decomposition reaction of ammonium perchlorate (AP), a solid rocket propellant oxidizer, was evaluated. To evaluate the effectiveness of this nano TiO2 catalyst, the activation energy of the catalyzed decomposition reactions of AP was computed by a non-linear integral isoconversional method. The calculated activation energy value was then compared with that of non-catalyzed AP decomposition reactions. The catalyzed AP decomposition showed an unaffected low temperature decomposition (LTD) at the extent of conversion (α) between 0 and 0.30. Further, a characteristic slowdown and a nanocatalyst influenced high temperature decomposition (HTD) at α between 0.35 and 1 was observed. The possible reasons for the catalytic effect of TiO2 nanoparticles on the HTD of AP are discussed based on the fact that the exposed cations and anions on the transition metal oxide nanoparticle surface act as acid–base site pairs and adsorb gaseous reactive molecules formed during the LTD of AP.

Hydrogen Peroxide Decomposition in Ammonia Solutions

The decomposition of in ammonia hydroxide peroxide mixtures (APM) have been studied as a function of metal‐ion weight concentration (0.1‐10 ppb range) and temperature. It has been found that the uncatalyzed self‐decomposition of is second order with an activation energy of 170 (±10) kJ/mol. Additionally, copper ions, which form mononuclear ammonia complexes catalyze the decomposition. Superimposed on the uncatalyzed reaction, a first order copper‐ion catalyzed decomposition with an activation energy of 84 (±2) kJ/mol has been measured. The iron‐ion catalyzed reaction is a mixture of first and second order. Due to the insolubility of Fe(III) it aggregates to large clusters or colloid particles. Higher concentrations of the large clusters shift the reaction kinetics from first order to second order. The first and second order iron‐ion catalyzed decomposition reactions have similar activation energies [65 (±4) and 71 (±4) kJ/mol] suggesting a similar primary reaction step. Furthermore, the effect of complexing agents has been evaluated. Substoichiometric amounts of diethylenetriamine‐NNN′N″N″‐penta(methylphosphonic) acid break down these iron clusters favoring the first order reaction at the expense of the second order reaction. Superstoichiometric amounts of the complexing agent completely inactivate the iron ions, but had no effect on the copper‐ion catalyzed decomposition reaction. © 1999 The Electrochemical Society. All rights reserved.

Hydrogen Peroxide Decomposition in Ammonia Solutions

The decomposition of in ammonia hydroxide peroxide mixtures (APM) have been studied as a function of metal‐ion weight concentration (0.1‐10 ppb range) and temperature. It has been found that the uncatalyzed self‐decomposition of is second order with an activation energy of 170 (±10) kJ/mol. Additionally, copper ions, which form mononuclear ammonia complexes catalyze the decomposition. Superimposed on the uncatalyzed reaction, a first order copper‐ion catalyzed decomposition with an activation energy of 84 (±2) kJ/mol has been measured. The iron‐ion catalyzed reaction is a mixture of first and second order. Due to the insolubility of Fe(III) it aggregates to large clusters or colloid particles. Higher concentrations of the large clusters shift the reaction kinetics from first order to second order. The first and second order iron‐ion catalyzed decomposition reactions have similar activation energies [65 (±4) and 71 (±4) kJ/mol] suggesting a similar primary reaction step. Furthermore, the effect of complexing agents has been evaluated. Substoichiometric amounts of diethylenetriamine‐NNN'N''N''‐penta(methylphosphonic) acid break down these iron clusters favoring the first order reaction at the expense of the second order reaction. Superstoichiometric amounts of the complexing agent completely inactivate the iron ions, but had no effect on the copper‐ion catalyzed decomposition reaction. © 1999 The Electrochemical Society. All rights reserved.

Heterogeneous catalyzed decomposition reactions of dichlorodifluoromethane in the presence of water on γ-alumina

The heterogeneous catalyzed decomposition of CCl 2F 2 (CFC-12) in the presence of water was investigated, employing γ-alumina as catalyst. The catalyzed hydrolysis reaction yields very high conversion degrees of CFC-12 in the first reaction stage. For a period of about 3 h there is a remarkable lack of balance between the amount of liberated HF and HCl owing to the uptake of HF by the oxide solid forming α-AlF 3. Only after about 3 h does the heterogeneous solid/gas reaction come to an end and then the HCl and the HF balance is equal. With the increasing fluoride content of the solid phase, the decomposition degree of CFC-12 decreases to a stable value of about 60% with respect to liberated CO 2. The conversion degree of CFC-12 seems to be higher but this is owing to the formation of CClF 3 (CFC-13), which is nearly stable under the conditions used. Mechanistic explanations are given for the formation of CClF 3 whether by dismutation reactions or owing to hydrofluorination reactions of CFC-12. Arguments are given about which mechanism might be the most probable. Furthermore, mechanistic hypotheses are concluded and discussed with respect to the processes at the catalyst surface on the basis of the experimental results.

A quantitative study on the growth of silicon whiskers from silane and germanium whiskers from germane

The impurity-induced nucleation and the kinetics of the growth of filamentary crystals of silicon and germanium from silane and germane respectively have been studied in a closed system. Silicon whiskers were grown on heated substrates at temperatures between 550 and 900 °C, germanium whiskers at temperatures between 300 and 500 °C, both at hydride pressures between 5 and 100 Torr, and with Au as impurity. Whisker growth was also obtained with Ag, Cu, Ni and Pd, but not with In, Sn and Bi. The rates of growth of the whiskers in the length direction increase with increasing substrate temperature and hydride pressure, and are of the order of a hundred times higher than the rates of thickness growth of whiskers and substrate. As compared with the non-impurity aided deposition of Si and Ge from the hydrides, where there is an exponential relation between deposition rate and reciprocal temperature, the effect of the growth stimulus at the tip is reflected in a decrease of the activation energy and an increase in the pre-exponential factor. In terms of the VLS mechanism the catalyzed decomposition reaction at the V-L interface is the rate-controlling step.