C. Mazzocchia

On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity

The α- and β-phases of NiMoO4 have been investigated with different techniques (X-ray diffraction, electrical conductivity, IR spectroscopy) in order to tentatively rationalise the different catalytic activities observed in the oxidative dehydrogenation of propane to propene. XRD analyses have shown that at 595 ° C, the β-phase is already present but a temperature of ∼ 700 ° C is required to obtain a full conversion into a pure β-phase. Electrical conductivity showed the presence of anionic vacancies. It is proposed that propene is formed by the reaction of propane with surface O2- anions. The β-phase is almost twice more selective in propene formation than the α-phase for comparable conversion at identical temperatures. This could derive from different oxygen environments on the active catalytic site.

The synthesis of acrolein and acrylic acid by direct propane oxidation with Ni–Mo–Te–P–O catalysts

Abstract Ni–Mo–Te–P–O systems were tested for the synthesis of acrolein and acrylic acid by direct oxidation of propane. The effects of the reaction variables and of the water vapour on the catalytic performances were examined. The addition of dopants, such as Te and P, improved the yields and selectivities of acrolein and acrylic acid.

Metal dispersion dependent selectivities for syngas conversion to ethanol on V2O3 supported rhodium

Abstract The influence of dispersion on the interactions of hydrogen and carbon monoxide with Rh/V2O3 has been investigated (transmission electron microscopy and temperature-programmed desorption). The catalysts having a 0.2% Rh loading were more highly dispersed (8–12A˚) than the catalysts with 1.0% Rh (35–40A˚). Up to 523 K a higher selectivity towards ethanol than towards carbon dioxide is observed upon decreasing the metal dispersion. The metal particle size is being evaluated as a factor of importance for carbon monoxide dissociation.

Hydrogenation of CO over Rh/SiO2-CeO2 catalysts: kinetic evidences

Abstract The CO hydrogenation over Rh/SiO 2 -CeO 2 was investigated kinetically in order to find the rate equation as a function of CO and H 2 partial pressures. Relative to previous findings obtained with Rh/SiO 2 a fairly higher dependence on adsorbed CO is evident. Together with additional evidences found by TPD/TPR and IR spectroscopy, this higher dependence has been tentatively associated to a CO in which both the carbon and the oxygen ends are bonded to Rh and Ce 3+ , respectively. The influence of the support has been emphasized in order to ascertain the role of CeO 2 (promoter) relative to Rh/SiO 2 . In agreement with previous findings we have found that with Rh/SiO 2 -CeO 2 catalysts, the promoter inhibits the total activity while favoring the formation of EtOH.

Oxidative dehydrogenation of ethane on the α and β phases of NiMoO4

Abstract The oxidative dehydrogenation of ethane on the α and β phases of NiMoO4 was studied, and the results compared with those previously obtained on propane in the 500–600°C range. A reaction mechanism is proposed in accordance with the surface properties, preliminary kinetic studies and catalytic tests with ethanol as a probe molecule.

Propane and isobutane oxidative dehydrogenation with K, Ca and P-doped α-, and β-nickel molybdate catalysts

While the catalytic performances of stoichiometric nickel molybdate in the oxidative dehydrogenation of isobutane into isobutene and methacrolein are improved by the addition of potassium oxides, the oxidation of propane to propene is mainly affected by calcium oxides. The selectivity towards the corresponding alkenes and specifically the methacrolein selectivity are also affected by the active catalyst phase and the oxygen/alkane ratio in the feed.

Thermal activation of typical oxidative dehydrogenation catalyst precursors belonging to the Ni−Mo−O system

NiMoO4 obtained by calcination of precursors has been shown to be a very effective catalyst for oxidative dehydrogenation of propane into propene. Preparation conditions and thermal decomposition of two precursors have been studied by TG-DTA, HTXRD, FFT-IR, and thermo-desorption coupled to mass spectroscopy in order to determine their composition and to define the best treatment to favour the oxidative dehydrogenation process. The selectivity and activity for propane transformation into propene are very different depending on the nature of the precursor and of the active phases obtained after thermal activation. The more selective high-temperature β phase of NiMoO4 has been obtained at a lower temperature (500°C) than previously reported (700°C).ZusammenfassungDurch Kalzinierung von Präkursoren hergestelltes NiMoO4 erwies sich als sehr wirkungsvoller Katalysator für die oxidative Dehydrogenisierung von Propan zu Propen. Mittels TG-DTA, HTXRD, FFT-IR und Thermodesorption/MS wurden die Herstellungsbedingungen und die thermische Zersetzung von zwei Präkursoren untersucht, um ihre Zusammensetzung zu ermitteln und um die beste Art zur Begünstigung des oxidativen Dehydrogenisierungsprozesses zu finden. Selektivität und Aktivität der Umwandlung von Propan zu Propen ist je nach Art des Präkursors und der nach thermischem Aktivieren erhaltenen aktiven Phasen sehr verschieden. Die selektivere Hochtemperatur β-Phase von NiMoO4 wurde bei einer niedrigeren Temperature (500°C) erhalten, als bis dahin beschrieben (700°C).

Heterogenized boron(III)-molybdenum(VI) mixed oxo derivatives as new bimetallic catalysts for cyclo-hexene liquid-phase epoxidation

Abstract The catalytic epoxidation of cyclohexene has been studied in the liquid phase using as catalysts molybdenum-boron mixed oxo derivatives supported on new polymeric resins. The binary system catalysts, in which the formation of B-O-Mo chemical bonds is suggested on the basis of spectral data, retain constant activity when recycled. Relative to conventional homogeneous molybdenum catalysts, no chemical degradation is observed.

Hydrogenation of CO over ZrO2-supported Rh catalysts: role of experimental parameters in modifying the C2H5OH/CH4 product ratio

The hydrogenation of CO over ZrO2-supported rhodium catalyst has been extensively investigated in an attempt to increase the C2H5OHCH4 ratio while minimizing CH3OH. Only one scheme has been found to account satisfactorily for the experimental rate equation determined by using CO and H2 partial pressure dependence. This scheme assumes the formation of a CHx moiety on the catalyst surface as the rate-determining step. Furthermore, in agreement with earlier findings, it is also consistent with the intermediate formation of acetaldehyde. Finally, the role of the support has been emphasized, as it has been found that ZrO2 significantly affects ethanol selectivity.

Sol-Gel Processing of Copper-Chromium Catalysts for Ester Hydrogenation

Copper chromite catalysts were prepared by using a new metal organic precursor, M(OR)n, which was dissolved in organic solvent, hydrolysed and condensed to form inorganic polymers containing M-O-M linkages. In the cases of Ba and Mn promotion, the corresponding metal oxide was admixed to the copper-chromium solution prior to gelification. After drying in helium atmosphere, the precursor was subjected to thermal treatment at different temperatures (373-873 K) and in different atmospheres (air, nitrogen or hydrogen). Both the catalysts and the industrial Engelhard catalyst were characterized by various techniques (TG-DTA, HTXRD, IR, BET, metallic copper surface area and porosimetry measurements) and evaluated for ester hydrogenation.