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The thermodesorption spectra of hydrogen from coprecipitated catalysts (70-x)NiO-xMgO-30Al(2)O(3) (x = 0-50%(wt)) are reported. The catalysts were calcined at 400 degrees C and reduced with H(2) at 20-800 degrees C and for 3 h at 800 degrees C. NiO reduction degree was between 49.3 and 92.1%. The active surface areas changed from 8.4 to 32.4 m(2)/g whereas mean size of nickel crystallites was between 3.7 and 9.7 nm. The TPD spectra were next analyzed in order to determine the adsorption energy distributions functions. To obtain these functions a theoretical model of adsorption/desorption kinetics based on the statistical rate theory (SRT) was applied. This approach allows for determination of the adsorption energy at nonequilibrium conditions as well as at quasiequilibrium conditions. The resulting distribution functions reveal the presence of two main bands of adsorption energy. Some correlation is found between the determined distributions of adsorption energy and the size of nickel crystallites determined using the XRD method. The presence of MgO favors creation of high energy adsorption sites on Ni crystallites.

This work deals with the design of a nanocontainer that is able to carry hydrolytically labile molecules like carmustine, undergo selective endocytosis by cancer cells, and de-encapsulate its cargo on demand by application of an external magnetic field. The molecular architecture of the nanocontainer does not differ much from the already known and experimentally characterized systems designed for the realization of stimuli-responsive anticancer drugs carriers. It comprises a carbon nanotube (for the encapsulation of drug molecules in its inner volume) and functionalized nanoparticles, which act as caps to the nanotube and are linked with the nanotube tips by linkers containing hydrazone bonds fragments. At acidic pH, the hydrazone bonds hydrolyze, and the nanotube should be uncapped as the nanoparticles are no longer covalently linked with the nanotube. This simple mechanism is, however, not always operational due to the significant role of nonbonded interactions between the nanotube and the nanoparticles. Our model utilizes the functionalized magnetic nanoparticles as caps to the nanotube, and therefore the nanocontainer becomes sensitive to the external magnetic field. In order to study how the magnetic field affects the state of the nanocontainer, we developed a dedicated molecular dynamics code for the description of the magnetization reversal and coupled it with the standard code of the Newtonian dynamics. The obtained results imply that very small magnetic nanoparticles produce too weak torques on the nanoparticles, and therefore no changes in the molecular structure of the nanocontainer occur. On the other hand, larger nanoparticles with radii > ∼35 Å absorb huge amounts of energy from the magnetic field and produce rapid turns of the nanoparticles. This leads to the uncapping of the nanotube and de-encapsulation of the drug molecules. Moreover, the system containing magnetic nanoparticles can additionally realize magnetic hyperthermia and can be visualized in magnetic resonance imaging. Therefore, the proposed architecture of the nanocontainer represents very promising and useful construction of a stimuli-responsive drug carrier.

This article deals with a quantitative analysis of thermodesorption spectra of ammonia: a technique commonly applied to study the surface acidity of solids. The method used for determination of adsorption energy distributions of ammonia is the same as that published recently for the case of hydrogen thermodesorption (Panczyk, T.; et al. Langmuir 2005, 21, 7311). The developed theoretical expression describing the thermodesorption process is based on the statistical rate theory (SRT) and its analysis leads to the conclusion that majority of thermodesorption processes, carried out under flow conditions, are in fact quasi-equilibrium ones. Similar conclusion has already been drawn by some authors applying the classical absolute rate theory (ART) for analysis of thermodesorption data. This conclusion has important practical consequences. Namely, it greatly simplifies the quantitative analysis of thermodesorption processes since there is no need to use any kinetic approaches to that purpose. The quantitative analysis of thermodesorption spectra can thus be based on commonly accepted relations following from equilibrium thermodynamics. It is worth noting that in quasiequilibrium conditions either the SRT or the ART lead to this same expression with only a slightly different meaning of some constants. Thus, in quasiequilibrium conditions there is no need to decide which theoretical approach should be applied. As an illustration, the ammonia thermodesorption spectra from the modified nickel catalysts are analyzed. The catalysts were prepared by the coprecipitation method and differ by the amount of MgO and NiO, whereas the amount of Al(2)O(3) is constant and equals 30%. It was stated that the presence of MgO reduces the number of acid centers corresponding to high values of ammonia adsorption energy.