On the Comparison of Small Nitrogen and Phosphorus Oxide Cages

Ab initio electronic structure calculations, including a natural bond orbital (NBO) analysis, are employed to compare the stabilities of larger nitrogen oxide cages and phosphorus oxide cages relative to the cage compound c‐N₂O₃ , which has been previously investigated as a potential energetic oxidizer. The larger N O cages, c‐N₂O₆ and c‐N₄O₆ exhibit less internal strain but have significantly lower barriers to decomposition of 1.9 kJ mol⁻¹ and 5.6 kJ mol⁻¹ respectively, compared to 37.6 kJ mol⁻¹ for c‐N₂O₃, at the MP2/aug‐cc‐pVDZ level of theory. In contrast, the phosphorus oxide cage c‐P₂O₃ exhibits similar internal strain but has a significantly larger barrier to decomposition of 40.2 kJ mol⁻¹ compared to the 24.4 kJ mol⁻¹ of c‐N₂O₃ at CCSD(T)/CBS(Q‐5). Furthermore, NBO analysis shows that the P O bond is more ionic in nature compared to the N O bond. The reduced degree of ionic character leads to the kinetic instability of the nitrogen oxide cages and therefore renders them impractical as energetic oxidizers.     

Tetrakis(nitratoxycarbon)methane (Née CLL‐1) as a Potential Explosive Ingredient: a Theoretical Study

Ab initio electronic structure calculations at the MP2/cc‐pVTZ level predict the vibrational stability of the theoretical molecule tetrakis(nitratoxycarbon)methane, designated CLL‐1. The gas phase enthalpy of formation, predicted to be +1029.3 kJ mol⁻¹ using the G3(MP2) method, and the estimated density of 1.87 g cm⁻³ are used to predict the explosive performance properties using the equilibrium thermochemical code CHEETAH. The predicted detonation velocity (8.61 km s⁻¹) and pressure (33.1 GPa) are similar to those of RDX, but with a significantly higher detonation temperature (6740 K). Finally, the stability of this theoretical molecule is investigated by calculating the lowest energy unimolecular decomposition pathways of the HCO₃N model compound as well as barriers to rearrangement upon interaction of two HCO₃N molecules.     

Substituent Effects on Thermodynamic and Detonation Properties of Polynitrobenzenes

Density functional theory (DFT) calculations were performed for a series of polynitrobenzene derivatives. Some nitrobenzenes with amino groups attached were also investigated as a benchmark or as a precursor. Heats of formation (HOF) were evaluated. The isodesmic reactions used for the prediction of HOFs are of permutation type in terms of the substituents. The HOFs increase non‐additively with increasing number of nitro groups. The attachment of the amino groups to polynitrobenzenes dramatically decreases the HOF. The HOF of hexanitrobenzene (HNB) is 344.05 kJ mol⁻¹ at the B3LYP/6‐311+G** level. This value is much larger than that of the widely used 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), which engenders HNB a large chemical energy of detonation. The strengths of the group interactions were analyzed according to the disproportionation energy. The nearest‐neighbor interactions in polynitrobenzenes are in the range of 27.20–55.90 kJ mol⁻¹. The energy barrier for the internal rotation of nitro group in nitrobenzene is 24.6 kJ mol⁻¹. However, the energy barrier for the internal rotation of 2‐position nitro group of 1,2,3‐trinitrobenzene is as large as 216.3 kJ mol⁻¹. The chemical energies of detonation for polynitrobenzenes with three or more nitro groups are over 6000 J g⁻¹. Pentanitroaniline and HNB have good performances in terms of detonation velocity and pressure.     

Triazidotrinitro Benzene: 1,3,5‐(N3)3‐2,4,6‐(NO2)3C6

Triazidotrinitro benzene, 1,3,5‐(N₃)₃‐2,4,6‐(NO₂)₃C₆ ( 1 ) was synthesized by nitration of triazidodinitro benzene, 1,3,5‐(N₃)₃‐2,4‐(NO₂)₂C₆H with either a mixture of fuming nitric and concentrated sulfuric acid (HNO₃/H₂SO₄) or with N₂O₅. Crystals were obtained by the slow evaporation of an acetone/acetic acid mixture at room temperature over a period of 2 weeks and characterized by single crystal X‐ray diffraction: monoclinic, P 2₁/c (no. 14), a=0.54256(4), b=1.8552(1), c=1.2129(1) nm, β=94.91(1)°, V=1.2163(2) nm³, Z=4, ϱ=1.836 g⋅cm⁻³, R_all =0.069. Triazidotrinitro benzene has a remarkably high density (1.84 g⋅cm⁻³). The standard heat of formation of compound 1 was computed at B3LYP/6‐31G(d, p) level of theory to be ΔH°_f=765.8 kJ⋅mol⁻¹ which translates to 2278.0 kJ⋅kg⁻¹. The expected detonation properties of compound 1 were calculated using the semi‐empirical equations suggested by Kamlet and Jacobs: detonation pressure, P=18.4 GPa and detonation velocity, D=8100 m⋅s⁻¹.     

Kinetics of Decomposition of Energetic Ionic Liquids

The Arrhenius‐type reaction rate parameters for the initiation reactions governing the thermal decomposition of several energetic ionic liquids (EILs) were determined by numerical techniques. The compounds chosen for this purpose were the energetic 4‐amino‐1,2,4‐triazolium nitrate (4ATN) and 1‐hydroxyethyl‐hydrazinium nitrate (HEHN). The supplementary compounds studied for comparison were 4‐amino‐1,2,4‐triazolium chloride (4ATCl) and ammonium nitrate (AN). The reaction rate parameters were obtained by an evolutionary genetic algorithm (GA) that compared the difference between the experimental and simulated species evolution profiles from the decomposition process. The experimental data were generated by confined rapid thermolysis (CRT). The decomposition process was simulated by applying conservation equations to the condensed and gas phases individually. The optimization module recovered the experimental species profiles with reasonable accuracy for all the compounds studied. The processes governing the decomposition of these energetic compounds were found to be autocatalytic in nature, and the autocatalytic agents were the strong acids generated by the initial decomposition step. The activation energy and pre‐exponential factor for the unimolecular decomposition step for 4ATN, HEHN, and 4ATCl were 167–188 kJ mol⁻¹ and 10¹⁶ s⁻¹, respectively, similar to previously determined values for AN.     

Structural and Preliminary Explosive Property Characterizations of New 3,4,5‐Triamino‐1,2,4‐triazolium (Guanazinium) Salts

Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen‐content heterocycle 3,4,5‐triamino‐1,2,4‐triazole and resulting in its picrate and azotetrazolate salts. 3,4,5‐Triamino‐1,2,4‐triazolium picrate (1) and bis(3,4,5‐triamino‐1,2,4‐triazolium) 5,5′‐azotetrazolate (2) were characterized analytically and spectroscopically. X‐ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6–31G(d, p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (Δ_cH (1) =−3737.8 kJ mol⁻¹, Δ_cH (2) =−4577.8 kJ mol⁻¹) and the standard enthalpy of formation (Δ_fH° (1) =−498.3 kJ mol⁻¹, (Δ_fH° (2) =+524.2 kJ mol⁻¹). The detonation pressures (P (1) =189×10⁸ Pa, P (2) =199×10⁸ Pa) and detonation velocities (D (1) =7015 m s⁻¹, D (2) =7683 m s⁻¹) were calculated using the program EXPLO5.     

A New Energetic Salt Semicarbazide 5‐Dinitromethyltetrazolate: A Promising Explosive Alternative

The design and synthesis of new environmentally friendly energetic materials with excellent performance and reliable safety have received considerable attention. A new energetic salt of semicarbazide 5‐dinitromethyltetrazolate (SCZ ⋅ DNMZ) was synthesized by using semicarbazide and 5‐dinitromethyltetrazolate (DNMZ) as raw materials, and fully characterized by using elemental analysis, FT‐IR spectroscopy, ¹H, ¹³C, and ¹⁵N nmR and mass spectrometry. The monocrystal of the salt was obtained and the structure was determined by X‐ray single‐crystal diffractometer. Results show that it belongs to monoclinic space group P 2₁/c with a high density of 1.867 g cm⁻³. The thermal decomposition behavior was tested by DSC and TG‐DTG technologies; the non‐isothermal kinetic parameters for the salt were calculated. The enthalpy of formation for the salt is directly dependent on the combustion heats data with a result of 341.5 kJ mol⁻¹, which is about three times higher than that of RDX. The detonation pressure (P ) and detonation velocitiy (D ) of the salt were determined as 8931 m s⁻¹ and 36.2 GPa, which are also higher than that of RDX. The impact sensitivity was tested with a result of 10.8 J. We can draw a safe conclusion that the salt has provided a promising future by using as a kind of explosive alternative. The discovery also contributes significantly to the expansion and application of the N‐heterocyclic compounds applied as energetic materials.     

Thermal Decomposition Research on 1,5‐Diazabicyclo[3.1.0] Hexane (DABH) as a Potential Low‐toxic Liquid Hypergolic Propellant

1,5‐Diazabicyclo[3.1.0] hexane (DABH) was found a potential hypergolic liquid propellant. The physical and energetic properties of DABH, 2‐(dimethylamino) ethyl azide (DMAZ), and monomethyl hydrazine (MMH) were compared. The ignition delay time of DABH with nitrogen tetroxide was 1 ms, which was shorter than DMAZ and similar with MMH. The toxicology experiment showed that half lethal dose (LD₅₀) of DABH was 621.0 mg kg⁻¹, which suggested that DABH was promising to be used as low‐toxic liquid propellant. Thermal decomposition experiments showed that the apparent activation energy (E ) was about 66.3 kJ mol⁻¹. The thermal decomposition calculated results from Madhusudanan‐Krishnan‐Ninan integration, Satava‐Sestak integration and Achar differential methods were compared and the pre‐exponential factor were obtained.     

Influence of Annealing on Mechanical αc‐Relaxation of Isotactic Polypropylene: A Study from the Intermediate Phase Perspective

The influence of annealing on mechanical α_c‐relaxation of isotactic polypropylene (i PP) is investigated. In the sample without annealing, polymer chains in the intermediate phase are constrained by crystallites with a broad size distribution, leading to one α_c‐relaxation peak with activation energy (E _a) of 53.39 kJ mol⁻¹. With an annealing temperature between 60 and 105 °C imperfect lamellae melting releases a part of the constraining force. Consequently, two α_c‐relaxation peaks can be observed (α_c1‐ and α_c2‐relaxation in the order of increasing temperature). Both relaxation peaks shift to higher temperatures as annealing temperature increases. E _a of α_c1‐relaxation decreases from 38.43 to 35.55 kJ mol⁻¹ as the intermediate phase thickness increases from 2.0 to 2.2 nm. With an annealing temperature higher than 105 °C, a new crystalline phase is formed, which enhances the constraining force on the polymer chains. So the α_c1‐relaxation peak is broadened and its position shifts to a higher temperature. Moreover, the polymer chains between the initial and the newly formed crystalline phase are strongly confined. Therefore, the α_c2‐relaxation is undetectable. E _a of α_c1‐relaxation decreases from 23.58 to 13.68 kJ mol⁻¹ as the intermediate phase thickness increases from 2.3 to 3.0 nm.     

Hypergolic Behavior of Pyridinium Salts Containing Cyanoborohydride and Dicyanamide Anions with Oxidizer RFNA

A series of low‐cost, pyridinium cation‐based hypergolic ionic liquids (HIL) containing amine, butyl, or allyl substituents with cyanoborohydride [BH₃CN]⁻ and dicyanamide [DCA]⁻ anions were developed and characterized. The investigated physicochemical properties include melting and decomposition temperature, viscosity, density, heat of formation (ΔH_f) and specific impulse (I_sp). The ignition delay (ID) of all HILs was tested with the oxidizer RFNA. The HIL, 1‐allyl 4‐amino pyridinium dicyanamide, exhibited highest density (1.139 g cm⁻³) amongst the known pyridinium HILs. The heats of formation predicted on the basis of Gaussian 09 suit programs were within the range of − 30 to 356 kJ mol⁻¹. The structure of HIL, 1‐butyl 4‐aminopyridinium cyanoborohydride, was examined by single‐crystal X‐ray diffraction, which revealed hydrogen bonding between anion and cation as N1−H1N ⋅⋅⋅ N3=2.07 Å, N1−H2N ⋅⋅⋅ H1B1=2.18 Å, and N1−H2N ⋅⋅⋅ H2B1=2.21 Å, respectively. HIL (1‐allyl 4‐aminopyridiniun cyanoborohydride) exhibited highest I_sp of 228 s amongst the designed series.     

Combustion Effects of Nitrofulleropyrrolidine on RDX‐CMDB Propellants

The effect of N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF) on the decomposition characteristics of hexogen (RDX) was investigated using differential scanning calorimetry (DSC). The results show that mNPF can accelerate the decomposition of RDX, the peak temperature (T_p) of the exothermal decomposition is reduced by 6.4 K, and the corresponding apparent activation energy (E_a) is decreased by 8.7 kJ mol⁻¹. N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF), carbon black (CB), and C₆₀ were used as combustion catalysts to improve the combustion performance of a composite modified double‐base propellant containing RDX (RDX‐CMDB). The burning rate experimental results show that mNPF has a stronger catalytic effect than C₆₀ and CB. The magnitude of the effect of the three carbon substances on the enhancement of the burning rate is as follows: mNPF>C₆₀>CB. The catalytic effects of different contents of mNPF on the burning rates of RDX‐CMDB propellants were also studied, and the results show that the burning rates of RDX‐CMDB propellants are improved with increasing mNPF content. The plateau burning rate of a RDX‐CMDB propellant can be increased to 19.6 mm s⁻¹ when 1.0 % mNPF is added, and the corresponding plateau combustion region occurs at 8–22 MPa.     

Iodine Pentoxide Nano‐rods for High Density Energetic Materials

The iodine pentoxide is one of the most advanced oxidizers for nanostructured energetic formulations among the thermites due to the highest energy release per volume 25.7 kJ cm⁻³. The size and shape of iodine pentoxide particles have a strong impact on the pressurization rates during the reaction. Although micro‐sized iodine pentoxide particles are commercially available, nano‐sized particles, which are desired for various nano‐energetic applications, are not available on the market. Conventional wet chemical methods are unable to produce iodine pentoxide nanoparticles due to high solubility in water. In this study, we demonstrate fabrication of iodine pentoxide nano‐rods by high energy mechanical treatment of micro‐sized I₂O₅ particles. Tuning the energy dose in high‐energy ball milling is allowing to produce I₂O₅ nano‐rods with diameter of 50–100 nm and length of 300–600 nm. The produced nano‐rods exhibited 10 % smaller decomposition energy compared to the precursor of micro particles. The experiments showed that the nano‐energetic materials prepared with nano‐sized I₂O₅ rods have pressure discharge value of 43.4 MPa g⁻¹ which is two times higher than using commercial iodine pentoxide particles.     

Kinetics of Bu‐NENA Evaporation from Bu‐NENA/NC Propellant Determined by Isothermal Thermogravimetry

Bu‐NENA (N‐butyl‐N‐nitratoethyl nitramine) base propellants have versatile qualities, such as, higher energy, reduced sensitivity, and enhanced mechanical properties. The evaporation of Bu‐NENA, which takes place in the propellant grains in the course of time, can reduce the physical properties of the propellants, weaken the propellant grains, cause the propellants to crack at stress‐concentrated points, and finally result in unfavorable increases or fluctuations of the burning rate and poor performance of the rocket motor. In this study, the evaporation of Bu‐NENA from a double base propellant was investigated using isothermal thermogravimetry. The results showed that the entire process of Bu‐NENA evaporation complied with the power law of evaporation rate with time. The values of kinetic parameters of Bu‐NENA evaporation were calculated: E _vap=67.68 kJ mol⁻¹ and A _vap=1.57×10⁵ s⁻¹. In comparison, the values of NG (nitroglycerin) evaporation were determined: E _vap=69.68 kJ mol⁻¹ and A _vap=1.33×10⁶ s⁻¹. The value of the activation energy of Bu‐NENA evaporation was close to that of NG, but the pre‐exponential factors differed by an order of magnitude. The evaporation of Bu‐NENA followed zero‐order kinetics at the early stage, and the enthalpy of Bu‐NENA evaporation was calculated to be 69.75 kJ mol⁻¹ according to Langmuir and Clausius‐Clapeyron equations.     

Thermochemical,Sensitivity and Detonation Characteristics of New Thermally Stable High Performance Explosives

The M06‐2X/6‐311G(d,p) and B3LYP/6‐311G(d,p) density functional methods and electrostatic potential analysis were used for calculation of enthalpy of sublimation, crystal density and enthalpy of formation of some thermally stable explosives in the gas and solid phases. These data were used for prediction of their detonation properties including heat of detonation, detonation pressure, detonation velocity, detonation temperature, electric spark sensitivity, impact sensitivity and deflagration temperature using appropriate methods. The range of different properties for these compounds are: crystal density 1.51–2.01 g cm⁻³, enthalpy of sublimation 346.4–424.7 kJ mol⁻¹, the solid phase enthalpy of formation 500.4–860.6 kJ mol⁻¹, heat of detonation 13.64–17.57 kJ g⁻¹, detonation pressure 33.0–37.0 GPa, detonation velocity 8.5–9.5 km s⁻¹, detonation temperature 5488–6234 K, electric spark sensitivity 7.89–9.47 J, impact sensitivity 21–38 J, deflagration temperature 560–586 K and power [%TNT] 207–276. The results show that two novel energetic compounds N,N′‐(diazene‐1,2‐diylbis(2,3,5,6‐tetranitro‐4,1‐phenylene))bis(5‐nitro‐4H‐1,2,4‐triazol‐3‐amine) (DDTNPNT3A) and 1,1′‐(diazene‐1,2‐diylbis(2,3,5,6‐tetranitro‐4,1‐phenylene))bis(3‐nitro‐1H‐1,2,4‐triazol‐5‐amine) (DDTNPNT5A) can be introduced as thermally explosives with high detonation performance.     

Effects of N-oxide on the thermal stability of energetic materials: A case study of 2,6-Diamino-3,5-dinitropyrazine-1-oxide

Finding new insensitive high explosives has been the focus of the energetic materials community in recent decades. To accelerate the discovery process, it is necessary to elucidate the relationship between molecular structure and the performance of explosives. In this regard, the effects of N-oxide groups, commonly introduced to increase the energy density of explosives, on the thermal stability of explosives were investigated by comparing the thermal behaviors of a typical energetic N-oxide, ANPZO, and its analogue ANPZ. The presence of N-oxide facilitated the thermal decomposition of ANPZO thoroughly and suppressed its sublimation to a certain extent. Compared to ANPZ, the introduction of N-oxide increased the thermal enthalpy, reduced the solid residues, and shortened the acceleration period of thermal decomposition of ANPZO. Additionally, the sublimation rate and vapor pressure of ANPZO were lower than those of ANPZ. The enthalpy of sublimation for ANPZO was 175.1 kJ mol⁻¹, compared to 135.2 kJ mol⁻¹ for ANPZ. The effects of N-oxide on the thermal decomposition and sublimation are attributed to its contribution to the augmentation of oxygen sources and intermolecular interactions, respectively. This study provides further insight into the relationship between the N-oxide group and the performance of explosives, which could be beneficial for the design and application of new explosives.     

Synthesis,Crystal Structure,and Thermal Behavior of 3‐(4‐Aminofurazan‐3‐yl)‐4‐(4‐nitrofurazan‐3‐yl)furazan (ANTF)

The energetic material 3‐(4‐aminofurazan‐3‐yl)‐4‐(4‐nitrofurazan‐3‐yl)furazan (ANTF) with low melting‐point was synthesized by means of an improved oxidation reaction from 3,4‐bis(4′‐aminofurazano‐3′‐yl)furazan. The structure of ANTF was confirmed by ¹³C NMR spectroscopy, mass spectrometry, and the crystal structure was determined by X‐ray diffraction. ANTF crystallized in monoclinic system P2₁/c, with a crystal density of 1.785 g cm⁻³ and crystal parameters a=6.6226(9) Å, b=26.294(2) Å, c=6.5394(8) Å, β=119.545(17)°, V=0.9907(2) nm³, Z=4, μ=0.157 mm⁻¹, F(000)=536. The thermal stability and non‐isothermal kinetics of ANTF were studied by differential scanning calorimetry (DSC) with heating rates of 2.5, 5, 10, and 20 K min⁻¹. The apparent activation energy (E_a) of ANTF calculated by Kissinger's equation and Ozawa's equation were 115.9 kJ mol⁻¹ and 112.6 kJ mol⁻¹, respectively, with the pre‐exponential factor lnA=21.7 s⁻¹. ANTF is a potential candidate for the melt‐cast explosive with good thermal stability and detonation performance.     

Solubility of potassium ferrate in 12 M alkaline solutions between 20°C and 60°C

The solubility of potassium ferrate (K₂FeO₄) was measured in aqueous solutions of NaOH and KOH of total concentration 12 M containing various molar ratios of KOH:NaOH in the range 12:0 to 3:9. Several analytical methods were tested for the determination of ferrate concentration. The final method chosen consisted of potentiometric titration of the ferrate sample with an alkaline solution of As₂O₃. The assumption was made that ferrate dissociates in concentrated KOH solutions predominantly to KFeO₄⁻. The solubility constant, S, defined as the product of the molar concentration of the potassium ion, K⁺, and the ferrate anion, KFeO₄⁻, was found to be 0·044 ± 0·006 mol² dm⁻⁶ for 20°C, 0·093 ± 0·004 mol² dm⁻⁶ for 40°C and 0·15 ± 0·09 mol² dm⁻⁶ for 60°C. From these results the heat of dissolution of K₂FeO₄ was calculated as −14·3 kJ mol⁻¹. At 60°C the enhanced decomposition of the ferrate at the higher temperature led to a greater deviation in solubility values compared with data for either 20°C or 40°C.     

Pyrolysis and thermo‐oxidative degradation of polycyclopentadiene

Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500–950°C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E_a) was obtained from an Arrhenius‐type plot using the concentration of the product ethylene (C₂) at different pyrolysis temperatures and the value was found to be 138 kJ mol⁻¹. Thermo‐oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700°C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635–641, 2000     

Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT‐NO3)

The enthalpies of combustion (Δ_combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO₃) were determined experimentally using oxygen bomb calorimetry: Δ_combH(DNB)=5195±200 kJ kg⁻¹, Δ_combH(HDAT‐NO₃)=7900±300 kJ kg⁻¹. The standard enthalpies of formation (Δ_fH°) of DNB and HDAT‐NO₃ were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ_fH°(DNB)=−353 kJ mol⁻¹, −1 829 kJ kg⁻¹; Δ_fH°(HDAT‐NO₃)=+254 kJ mol⁻¹, +1 558 kJ kg⁻¹. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT‐NO₃ were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66 mm μs⁻¹, P(DNB)=33.9 GPa, D(HDAT‐NO₃)=8.77 mm μs⁻¹, P(HDAT‐NO₃)=33.3 GPa.     

A Study of the Activated Decomposition of CO2 on the Cu Component of a Cu/ZnO/Al2O3 Catalyst

The decomposition of CO₂ over the Cu component of two ZnO/Al₂O₃ supported Cu catalysts, having different Cu areas, has been studied over the temperature range 393–513 K. The time dependence of the evolution of CO from a CO₂/He stream (10% CO₂, 101 kPa) which was dosed continuously over the catalyst showed two peak maxima, the first of which moved to shorter times on raising the temperature. The activation energy for the decomposition of CO₂ on the ZnO/Al₂O₃ supported polycrystalline copper was obtained from a plot of the logarithm of the time to the peak maximum of the first peak against the reciprocal of the dosing temperature. The value so obtained was 83±10 kJ mol^-1 (catalyst A) and 86±10 kJ mol^-1 (catalyst B) for fresh catalysts reduced in H₂ at 513 K. This value fell to 49 ±4 kJ mol^-1 (catalyst A) and 55±5 kJ mol^-1 (catalyst B) after CO reduction at 473 K of the Cu which had been oxidised by the decomposition of the CO₂. This lowering of the activation energy for the second CO₂ decomposition is considered to be due to the original morphology of the Cu not being restored by reduction in CO after the oxygen-driven reconstruction of the Cu deriving from the decomposition of the CO₂.