The use of a Pd/C catalyst in the liquid phase hydrogenation of various aromatic nitriles (benzonitrile, benzyl cyanide, 3-phenyl propionitrile and cinnamonitrile) has been studied in order to assess the effectiveness of this type of catalyst for this class of reaction. On modifying the nitrile substituent and upon introducing conjugation, varying degrees of conversion are observed. For benzyl cyanide and 3-phenylpropionitrile, incomplete mass balance profiles are linked to spill-over to the carbon support. In the case of benzonitrile hydrogenation, a hydrogenolytic step leads to a loss of selectivity to the primary amine to yield toluene with, ultimately, complete selectivity. Co-hydrogenation measurements on mixtures of benzonitrile and benzylamine indicate the presence of site-selective chemistry. Co-hydrogenation studies on mixtures of benzonitrile and benzyl cyanide highlight the competitive nature of the reaction system and, indirectly, establish a contribution from adsorbed imine species.

The hydrogenation of a number of C5 olefins (pent-1-ene, trans-pent-2-ene, cis-pent-2-ene, trans-1,3-pentadiene and a technical mixture of 1,3-pentadiene) over a 1% Pd/Al2O3 catalyst has been studied using in situ infrared spectroscopic methods to observe the changes in the gas phase molecules during the course of the reaction. Whereas trans-pent-2-ene is directly hydrogenated to pentane, the reaction profile for cis-pent-2-ene indicates a consecutive process involving the formation of gaseous trans-pent-2-ene as a reaction intermediate. Extending these studies to trans-1,3-pentadiene shows the terminal double bond to be hydrogenated first to produce trans-pent-2-ene in the gas phase, which is then subsequently hydrogenated to the alkane. A reaction scheme is proposed that defines how the molecules are partitioned between the gaseous and adsorbed phases. This scheme makes use of a previously postulated two-site adsorption model. Analysis of a technical grade of 1,3-pentadiene indicates the trans-monoene to play a significant role in the stepwise hydrogenation process.

Electrical plasmas operating at atmospheric pressure are in widespread use for materials processing and in related areas such as the characterisation of surfaces. The plasma sources are of many types. improvement of their design and optimisation of their operation require high quality diagnostic data. It is very helpful, for example, to have available information on the nature and energies of the active species produced in a source and impacting on a surface. The extension of diagnostic techniques first developed for work with low pressure plasmas to a wide variety of atmospheric plasmas is discussed, together with examples of the data obtainable.

The hydrochlorination of methanol over a commercial grade eta-alumina catalyst has been investigated via temperature-programmed reaction (TPR). Experiments were conducted over a temperature range of 295-1000 K using: (i) a methanol-only feed stream and (ii) a methanol/HCl mixed feed stream in a 1:1 mole ratio. Methanol-only studies showed activity for the formation of dimethyl ether (DME) above 450 K, consistent with temperature-programmed desorption studies. A rapid decline in DME activity and consumption of methanol at higher temperatures were observed and are attributed to a deactivation pathway, involving the conversion of methoxy species to surface formate species. At elevated temperatures these processes lead to the deposition of carbon on the substrate. The introduction of HCl to the reaction stream resulted in the formation of methyl chloride (MC) over a temperature range of 400-750 K. Relatively small quantities of DME by-product were also observed over a similar temperature range. The coincidence of the reaction profiles of both MC and DME imply that the same reactive methoxy species are involved in both processes. The rate of reaction for the formation of both products declines rapidly above 700 K. This is attributed to the methoxy decomposition pathway to formate and, ultimately, to carbon retention by the catalyst. The effect of carbon deposition was also investigated via a subsequent cooling process carried out immediately after TPR experiments. Reaction profiles showed comparable activity for the formation of both products with respect to initial TPR experiments. Taken together, these results indicate an optimum reaction temperature for the formation of methyl chloride from the hydrochlorination of methanol. At such temperatures, carbon deposition is minimized and high conversion is maintained. (c) 2006 Elsevier B.V. All rights reserved.

The interaction of HCl with an η-alumina catalyst has been investigated by a combination of diffuse reflectance infrared spectroscopy, temperature-programmed desorption and inelastic neutron scattering (INS) spectroscopy. Infrared spectra provide evidence for dissociative adsorption of HCl and for a process in which hydroxyl groups terminally bound to Al are replaced by chlorine. Temperature-programmed desorption experiments show HCl to desorb over the temperature range 350–>970K, indicating dissociative HCl adsorption to occur on a wide range of active sites. INS experiments show the residual alumina hydroxyl groups to exhibit an out-of-plane deformation feature, γ(OH), at ca. 200cm−1, while the in-plane deformation mode, δ(OH), is seen at ca. 1000cm−1. The formation of new surface hydroxyl groups via the adsorption of hydrogen chloride yields a δ(OH) feature that can be resolved into two bands at 990 and 1050cm−1. Hydrogen bonding within the alumina/HCl system is responsible for the observation of an Evans transmission window in the infrared spectrum, that occurs via a Fermi resonance interaction between (i) the ν(OH) mode of hydrogen bonded hydroxyl groups and chemisorbed water with (ii) the overtone of the δ(OH) mode of surface hydroxyl groups. The INS technique is able to discriminate among different hydroxyl group bonding geometries on the basis of the local symmetry of the active sites.