A carbon supported Pd catalyst is used in the liquid phase hydrogenation of the aromatic cyanohydrin mandelonitrile (C6H5CH(OH)CH2CN) to afford the primary amine phenethylamine (C6H5CH2CH2NH2). Employing a batch reactor, the desired primary amine is produced in 87% selectivity at reaction completion. Detection of the by-product 2-amino-1-phenylethanol (C6H5CH(OH)CH2NH2) accounts for the remaining 13% and closes the mass balance. The reaction mechanism is investigated, with a role for both hydrogenation and hydrogenolysis processes established.

The liquid phase hydrogenation of benzonitrile over a 5 wt % Pd/C catalyst using a stirred autoclave is investigated. The reaction conforms to a consecutive reaction sequence: first benzonitrile is hydrogenated to produce benzylamine, which subsequently undergoes a hydrogenolysis step to form toluene. Benzonitrile hydrogenation obeys first-order kinetics with an activation energy of 27.6 kJ mol–1. In contrast, the benzylamine hydrogenolysis stage obeys zero-order kinetics and exhibits an activation energy of 80.1 kJ mol–1. A 1 wt % Pd/Al2O3 catalyst is additionally examined, which is also seen to support hydrogenolysis activity alongside the hydrogenation pathway. Gas phase transmission infrared spectroscopic measurements of the hydrogenation of benzonitrile and benzylamine over the 1 wt % Pd/Al2O3 catalyst utilizing hydrogen and deuterium are undertaken, which enable reaction schemes incorporating adsorption geometries of intermediate adsorption complexes to be proposed.

The selective production of primary amines is a problem that plagues heterogeneously catalysed nitrile hydrogenation reactions. Whilst the target amine tyramine (HOC6H4CH2CH2NH2) is biochemically available through the action of enzymes, synthetic routes to this species are not widely reported. Here, a heterogeneously catalysed method is proposed that utilises a Pd/C catalyst to effect the selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor. The aforementioned selectivity issues are overcome by adjustment of various experimental parameters (hydrogen supply, agitation rate, temperature, use of an auxiliary agent) that result in improved catalytic performance, such that the desired tyramine salt (tyramine hydrogen sulphate) can be produced in quantitative yield. Accordingly, through consideration of the interconnectivity of hydrogenation and hydrogenolysis processes, a selective synthetic strategy is achieved with the findings suitable for extension to other substrates of this nature.

The origin and role of coke in ethylbenzene dehydrogenation over CrOx/Al2O3 has been studied. Ethylene is the main coke precursor; however coke from aromatic species is beneficial for styrene production.

The structural changes that occur in a FeOx/gamma-Al2O3 catalyst during the [GRAPHIC] dehydrogenation of ethylbenzene in a fluidized CREC Riser Simulator have been investigated. Chemical and morphological changes are observed to take place as a result of reaction. Electron microscopy reveals the formation of needle-like alumina structures apparently enclosing iron oxide particles. The formation of such structures at relatively low temperatures is unexpected and has not previously been reported. Additionally, X-ray diffraction and Mossbauer spectroscopy confirmed the reduction of the oxidation state of iron, from Fe2O3 (haematite) to Fe3O4 (magnetite). Iron carbides, Fe3C and epsilon-Fe2C, were detected by electron microscopy through electron diffraction and lattice fringes analysis. Carbon deposition (coking) on the catalyst surface also occurs. The observed structural changes are likely to be closely correlated with the catalytic properties of the materials, in particular with catalyst deactivation, and thereby provide important avenues for future study of this industrially important reaction.

The dehydrogenation of ethylbenzene to styrene is a highly important industrial reaction and the focus of significant research in order to optimise the selectivity to styrene and minimise catalyst deactivation. The reaction itself is a complex network of parallel and consecutive processes including cracking, steam-reforming and reverse water-gas shift (RWGS) in addition to dehydrogenation. The goal of this investigation is to decouple the major processes occurring and analyse how side-reactions affect both the equilibrium of ethylbenzene dehydrogenation and the surface chemistry of the catalyst. Studies have employed a CrOx/Al2O3 catalyst and reactions have been conducted at 500, 600 and 700 degrees C. The catalyst and reaction have been investigated using elemental analysis, temperature programmed oxidation (TPO), temperature-programmed desorption (TPD), Raman spectroscopy, THz time-domain spectroscopy (THz-TDS), X-ray photoelectron spectroscopy (XPS), in situ infrared spectroscopy and on-line gas chromatography and mass spectrometry. The reaction profile shows an induction time corresponding to a cracking regime, followed by a dehydrogenation regime. The cracking period involves the activation of CrOx/Al2O3 catalysts for dehydrogenation activity through a number of processes: cracking of ethylbenzene over acid sites; coke deposition; reduction of chromium from Cr(VI) to Cr(III); steam reforming activity over the reduced catalyst; and reverse water-gas shift reaction. Each of these processes plays a critical role in the observed catalytic activity. Notably, the presence of CO2 evolved from the reduction of chromium by ethylbenzene and from the gasification of the deposited oxygen-functionalised coke results in the dehydrogenation reaction becoming partially oxidative, i.e. selectivity to styrene is enhanced by coupling of ethylbenzene dehydrogenation with the reverse water-gas shift reaction. Ethylbenzene cracking, coke gasification, steam-reforming and reverse water-gas shift determine the relative quantities of CO2, CO, H-2 and H2O and hence affect the coupling of the reactions. Coke deposition during the cracking period lowers the catalyst acidity and may contribute to chromium reduction, hence diminishing the competition between acid and metal sites and favouring dehydrogenation activity.

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.

In the crystal structure of the title compound, C13H10O3, the mol­ecules form classical hydrogen-bonded carboxylic acid dimers [O⋯O = 2.651 (2) A]. These dimers are linked by C—H⋯π and π–π inter­actions to give a three-dimensional network.