P. Gronchi

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.

Dry reforming of CH4 with Ni and Rh metal catalysts supported on SiO2 and La2O3

Abstract The catalytic activities of Rh and Ni metals supported on SiO2 or La2O3 were compared at CH4+CO2 reforming conditions and performing catalytic tests and thermal analyses in thermodynamic conditions favourable for carbon deposition. The deactivation of both the metals deeply depend on the support. An increased CO production is obtained with lanthana but the comparison between Rh and Ni on carbon deposition base suggests that a positive effect could be reached only at low methanation activity.

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.

CARBON DEPOSITION IN METHANE REFORMING WITH CARBON DIOXIDE Dry reforming

Coke formation in the dry reforming of methane was studied using a thermobalance (TG) and with a catalytic microreactor in the temperature range 800–950 K. Silica-supported and lanthana-supported nickel catalysts were examined. The effects of process variables such as temperature and gas composition (He dilution, CH4/CO2 ratio) on the coke formation rate were determined. The reactivity of H2 on several kinds of carbon was also investigated. The morphology of the coke was studied by scanning electron microscopy (SEM). The induction times for coke formation were significantly affected by temperature and by the CO content in the feed gas. The results of catalytic tests were consistent with the TG measurements. The behaviour of SiO2 and La2O3 supported Ni catalysts agree with a mechanism in which the lanthana support plays an important role in the carbon deposition.

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.

Oxidative dehydrogenation of propane by continuous and periodic operating flow reactor with a nickel molybdate catalyst

Oxidative dehydrogenation of propane with nickel molybdate catalysts (αNiMoO4) has been investigated in flow reactors feeding the reactant gases continuously and periodically. The data obtained by the continuous operating system (COS) showed the determining role of lattice oxygen on the selectivity. Moreover, when only the lattice oxygen was consumed, very high propene selectivity was obtained.

Synthesis of nickel supported catalysts for hydrogen production by sol-gel method

SiO2 and Al2O3 supported Ni catalysts were synthesized in the form of xerogels: the SiO2 based materials were prepared starting from Ni propionate or glycolate salts and reacting them with tetraethoxysilane (TEOS) in propionic acid, Si(ethylene glycolate) or sodium silicate. The Al2O3 supported catalysts were prepared similarly from Ni propionate salts with Al iso-propoxide salts. Narrow metal particles and strong metal support interactions are observed in the sol-gel catalysts. The metal dispersion was higher for Al2O3 based materials than the SiO2 ones and it deeply depends on the Ni precursor for the silica supported Ni. Wet impregnated oxides with similar Ni loading have higher metal surface area than those from sol-gel processing. The influence of surface differences on the catalytic activity of the materials was studied following the CH4 and CO2 reaction in dry reforming conditions by pulse reaction tests.

Anodic oxidation and sol–gel coatings for corrosion and wear protection of AM60B alloy

Abstract In this paper a study on the corrosion and wear protection of AM60B magnesium alloy, by means of multilayer coating, is described. The coating mainly consists of a porous oxide layer MgO, produced by oxidation in microarc regime, and a single or multilayer top coat of SiOx produced by sol–gel technique and deposited by either a dip or spray coating method. The anodic oxidation pretreatment improves the adhesion of the sol–gel layers, which seal the porosity of MgO and improve corrosion protection. Furthermore, the multilayer coating significantly improves AM60B wear resistance. Scanning electron microscopy and radiofrequency glow discharge optical emission spectroscopy were used to assess surface morphologies and in depth elemental profiles of the coatings. Electrochemical polarisation tests and wear tests were performed to evaluate the corrosion resistance behaviour and the wear resistance of the coated magnesium alloys.

Isothermal Reduction Behaviour of Some Metal Molybdates. Selective light alkane oxydehydrogenation and/or olefins partial oxidation

The reduction profile of several unpromoted and promoted metal molybdate catalysts was investigated correlating their reducibility with the reactivity in catalysis.Using the stoichiometric α- and β-nickel molybdate compounds it was observed that the reduction rate was significantly affected by the nature of the phase. The results show thatβ-NiMoO4 phase led to a significant increase in the reduction rate with respect to α phase. The increased resistance to reduction by hydrogen due to the structure of the catalytic system is reported. It was found that there is a relationship between the reducibility of the catalysts and selectivity to dehydrogenation products, indicating that the lattice oxygen plays an important role in the reaction.The effect of MoO3, TeO2 and Te2MoO7 added to NiMoO4 systems onthe reducibility of the catalyst and on the propylene oxidation were also studied. It wasobserved that the reduction rate was significantly affected by the nature of the doping element. The results show that NiMoO4–MoO3 combination led toa significant increase of the reduction resistance of the nickel molybdate while TeO2 or Te2MoO7 addition increases its oxygen depletion rate.Ni–Mo–O systems (Mo/Ni>1) were found to favour low COx selectivity, high selectivity to C3H4O and C3H4O2 and good propylene conversion. In presence of TeO2 and Te2MoO7 doped Ni–Mo–O system both acrolein and propylene conversion were increased with respect to the undoped system. Ni–Mo–Te–O catalysts have been found to have a reducibility trend which fits well with the acrolein and acrylic acid formation from propylene oxidation in presence of molecular oxygen.

On the reactivity of K2O-, CaO- and P2O5-doped nickel molybdate catalysts in a periodic-flow reactor

The propane oxydehydrogenation with monolayer lattice oxygen of undoped and K2O–, CaO– and P2O5–NiMoO4 was investigated by using a periodic‐flow reactor (PFR). The influence of the nature and the extent of the promoter has been emphasized relative to the doped catalysts with respect to pure NiMoO4 phases. It was observed that calcium and potassium promoters satisfactorily enhance propylene selectivity, and phosphorus promoter specifically increases the total activity while maintaining the propylene selectivity. Evidence found by thermogravimetric (TG) analyses (oxygen depletion rate) has shown a dependence on lattice oxygen mobility due to the presence of promoters. This dependence has been correlated to the propane conversion while the propylene selectivity was attributed to the acid–base properties.