Showing papers on "Temperature-programmed reduction published in 1990"

Temperature-programmed reduction study of NiO–MgO interactions in magnesia-supported Ni catalysts and NiO–MgO physical mixture

Abstract: The reducibility of magnesia-supported nickel catalysts and NiO–MgO physical mixture has been studied by the temperature-programmed reduction (TPR) technique in the temperature range 373–1273 K. The influences of calcination temperature (673–1273 K), treatment time (1–48 h) and Ni loading (2.8–18 wt %) on NiO reduction have been evaluated. The TPR profiles of Ni/MgO catalysts reveal the presence of several forms of NiO, at the surface and in the near-surface regions (bulk-like) of the MgO, the reducibility of which is affected by the interaction strength between Ni2+ and underlying MgO support. A form of ‘unreacted’ NiO located on the MgO surface, which behaves as ‘bulk unsupported NiO’, was detected. Calcination at 673 K promotes a partial migration of Ni2+ ions into the MgO structure, which is enhanced by higher calcination temperatures, hindering the whole reducibility. At 1273 K an ‘ideal’ and non-reducible bulk NiO–MgO solid solution is formed. In contrast, the reducibility of the NiO–MgO physical mixture is slightly affected by calcination up to 1073 K and its TPR profile shows only a reduction peak shifted to higher T by calcination temperature. The different degree of interaction between NiO and MgO in supported and physically mixed systems has been explained in terms of different contact area arising from the preparation method. The importance of calcination time, in order to avoid erratic assessments due to unsteady states in the NiO–MgO reacting system, has been demonstrated. A linear correlation between the reducibility of Ni/MgO catalysts and the Ni loading was found, and was explained by inferring that higher Ni loading increases the fraction of ‘unreacted’ and ‘easy-reducible’ NiO.Experimental results indicate that TPR is a powerful technique for investigating the solid-state reaction between NiO and MgO.

Redox chemistry of highly dispersed rhodium in zeolite NaY

Abstract: NaY zeolite exchanged with [Rh(NH3)5Cl]2+ ions have been studied using temperature programmed oxidation (TPO), temperature programmed reduction (TPR), and Fourier transformed infrared spectroscopy. The TPO profiles show that ammine ligands in NaY encaged [Rh(NH3)5Cl]2+ are destroyed above 300 °C, whereas the Rh precursor ion remains intact after calcination at 200 °C. TPR profiles in conjunction with the COads IR spectra show that the reducibility of Rh by H2 is largely controlled by the concentration of the surface protons, i.e. Rh3++H2⇌Rh++2H+ Rh+ + 1/2H2⇌Rh0+H+

Temperature Programmed Reduction and Spectroscopic Studies of Reduction Behavior of fe/tiO2 Catalyst

Abstract: Fe/TiO2 catalyst was prepared by incipient wetness impregnation of TiO2 with aqueous solution of ferric nitrate. The reduction behavior of the catalyst was studied by temperature programmed reduction profiles, Mossbauer spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The results show that the reduction of Fe/TiO2 was accompanied by a phase transition of anatase to rutile titania. α-Fe2O3 was reduced to Fe3O4 in the initial reduction stage. Due to the strong support effect of TIO2, FeTiO3 was gradually formed as the reduction temperature reached 450°C. Complete reduction to the metallic Fe° particles occurred at temperatures higher than 670°C. The anatase-rutile transition was initiated by the reduced Ti3+ ions and led to the formation of TiOx. At higher reduction temperature, TiOx migrated to the surface of metallic Fe° particles forming FeTiOx in the so-called strong metal-support interaction (SMSI) state.