Authors:M. R. Granados-Uribe, F. J. Lona-Ramírez, C. Pérez-Pérez, J. Barajas-Fernández, V. Rico Ramírez, and G. González-Alatorre
of catalysis by nucleophiles and general base catalysis in the nitrosation reactions of 1,3-dialkylureas.
Proposed mechanism for the nitrosation of DRU catalyzed by carboxylic acids in an aqueous
Authors:R.V Salamon, É. Vargáné-Visi, Cs.D. András, Zs. Csapóné Kiss, and J. Csapó
L arock , R.C. , D ong , X. , C hung , S. , R eddy , C.K. & E hlers , L.E. ( 2001 ): Preparation of conjugated soybean oil and other natural oils and fatty acids by homogeneous transition metal catalysis . J. Am. Oil Chem. Soc. , 78
Authors:Dorina Chambre, Maria-Raluca Szabo, C. Popescu, and Cornelia Idiţoiu
Using a micro-calorimetrical DSC we have compared the acid-catalyzed inversion of sucrose in homogeneous and heterogeneous
systems. Acetic acid was chosen as catalyst for homogeneous system, and several carboxylic cationites were used as heterogeneous
catalysts. The kinetic apparent parameters (A, E, kap) for all the systems were calculated from DSC data with Friedmann’s method and catalytic constant, k323cat, was further inferred. We found that the specific catalyst efficiency, qcat, in heterogeneous system is over 5000 times higher than in case of homogeneous ones. The activity of heterogeneous carboxylic
systems is still about 30 times larger than those of a strong mineral acid in homogeneous catalysis.
The results indicate the high efficiency of heterogeneous systems for soft acid catalysis of the sucrose hydrolysis.
The reduction of bulk and supported copper oxide was investigated using Constant Rate-Temperature Programmed Reduction (CR-TPR)
and conventional linear heating rate TPR. Linear heating profiles indicated that the reduction of supported samples was more
facile than that of the bulk oxide. CRTA results revealed that both supported and bulk oxide samples were reduced via a mechanism
involving a nucleation step and/or auto-catalysis. The increased reducibility of the supported samples is attributed to a
higher dispersion which provides a larger reactive surface area and a high concentration of defects at which reduction is
Authors:T. Peev, A. Krylova, E. Kuzmann, and A. Vértes
Phase composition of Co-promoted ammonia synthesis catalysts has been studied by means of Mössbauer spectroscopy and X-ray diffractometry. Co-promoted catalysts have maximum activity at 5–7% CoO concentration. This result is associated with the substitution of 1–2 Fe atoms by Co-atoms per unit cell of the bcc -Fe lattice being the active phase for catalysis.
Authors:S. Ilie, S. Jipa, D. Ilie, R. Setnescu, J. Paun, I. Mihalcea, and A. Nicolescu
The present paper reports correlations between data obtained by the radiothermoluminescence (RTL) method and the catalytic activity of active aluminas. The correlations between the intensity of RTL signals, glow peak temperatures and activation energy obtained by RTL and the data referring to the history, catalytic activity and activation energy of the catalyzed reaction, require the use of RTL as a supplementary method in the characterization of catalysts. The results underline the role of structural defects in the catalyst (or support) on the catalysis as illustrated by the present model.
Authors:A. Kaddouri, R. Del Rosso, C. Mazzocchia, P. Gronchi, and D. Fumagalli
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.
Supported catalysts contain often only small amounts of active component(s) which renders their characterization difficult, particularly because they usually contain a substantial amount of water. Thermal analysis (TA) coupled with mass spectrometry (MS) offers an interesting potential for characterizing such material, various steps of catalyst preparation as well as crucial properties of fresh and used catalysts can be investigated. Some examples illustrating the versatility of TA-MS in catalysis research, such as solid-state reactions occurring upon exposure of the precursors or catalysts to reducing, oxidizing or inert atmosphere, are presented in this study. The combined use of TA and MS allows in many cases a much more detailed interpretation of the observed phenomena than could be achieved by one of these methods alone.