Regular and irregular catalyst packings are extensively used in the chemical industry for promoting mass transfer and chemical reaction between gas and liquid. Traditionally, randomly packed beds of catalyst particles operating in co-current downflow operation, often termed trickle-bed reactors, have been used because of the high mass-transfer rates achievable. More recently, structured supports are increasingly considered for use because of the potential improvements they offer with respect to, for example, the decoupling of heat-and mass-transfer phenomena, operation under reduced pressure drop conditions and at much higher gasrliquid Ž flow rates, and a greater resistance to attrition Irandoust and Andersson, 1988a,b; Irandoust et al., 1998; Kapteijn et al., . 1999 . Monoliths, which comprise a metal or ceramic structure with a large number of straight or parallel channels, are an example of such structured supports, and their use in solid-catalyzed gas-phase chemical reactions is well established. One example is the monolithic exhaust converter used throughout the automotive industry. In contrast, the application of monoliths to gas-liquid reactions is not well advanced and a significant research activity exists to provide the necessary understanding to enable reliable scale-up for process op-Ž . eration Nijhuis et al., 2001 . Undoubtedly, such efforts would be significantly aided if it were possible to develop an in-situ probe of the multiphase transport and reaction phenomena occurring within these porous structures. Magnetic resonance techniques show particular promise in this regard because of their ability to provide chemically-specific information on both the internal phase distribution and transport processes Ž . occurring within three-dimensional 3-D optically opaque systems.Visualization of gas-liquid flow in ceramic monoliths has Ž . previously been attempted by Mewes et al. 1999 using the capacitance tomography technique. While temporal resoluCorrespondence concerning this article should be addressed to L. F. Gladden. Ž tion of capacitance tomography is high 100 images per sec-. ond can be achieved , spatial resolution is relatively low with typical in-plane resolutions being 5᎐10% of the diameter of the system under investigation, thereby making impossible visualization of phase distribution within a single channel. In Ž . contrast, magnetic resonance imaging MRI has the poten-Ž . tial for relatively high spatial resolution say, 30᎐200 m , but the temporal resolution obtained for gas-liquid flow has to date been far too slow to visualize dynamic processes occurring in reactors. Time-averaged visualizations of singleand two-phase flow have been reported with data acquisition Ž times of minutes to hours Sederman et al., 1998;Tallarek et al. 1998;Johns et al., 2000; Sederman and Gladden, 2001; . Mantle et al., 2001 . Fast velocity imaging techniques have been reported which are able to acquire liquid velocity im-Ž ages in several minutes Seifert et al., 2000; Scheenen et al., . 2000 , but ...

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The hydrogenation of cinnamaldehyde was investigated using a 5% Pd/C catalyst in a 250 cm3 stirred tank reactor and 500 cm3 autoclave. The experiments were carried out at 273–343 K and 0·1–1·1 MPa. Non‐polar solvents, e.g. toluene, decane, methylcyclohexane, decalin, ether and heptane, and polar solvents such as methanol, ethanol, propan‐1‐o1, propan‐2‐ol, butan‐1‐ol and butan‐2‐ol were used to study the selectivity with respect to hydrocinnamaldehyde formation, the reaction kinetics and mass transfer. The additives, such as potassium acetate, ferrous chloride, ferrous sulphate and quinoline were incorporated into the catalyst in order to improve the catalyst selectivity, which was observed especially in the case of potassium acetate. © 1998 SCI

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