This Thesis describes how continuous flow reactors and heterogeneous catalysts have been used in conjunction with supercritical fluid solvents to develop a new process for carrying out catalytic organic reactions. The process exploits both the advantages of supercritical fluids (e.g. solvent tunability allowing facile product separation from the solvent) and heterogeneous catalysts and can be considered a 'Green' method of chemistry. Various reaction types have been explored, namely noble-metal catalysed hydrogenation reactions, supported-acid catalysed Friedel-Crafts alkylation reactions and supported-acid catalysed Friedel-Crafts acylation reactions. Chapter 1: Introduction This Chapter begins with an introduction to the concept of 'Green Chemistry' and its significance at the present time. The problems with the use of conventional solvents are highlighted, and examples of two 'greener' solvent systems - ionic liquids and supercritical fluids - are described. For each of these solvent systems, a brief review .of their use in more recent reaction chemistry is included. Chapter 2: Experimental This Chapter begins by describing the supercritical flow equipment developed at Nottingham in some detail, and includes equipment modifications which were made both to improve the effectiveness and safe operation of the equipment. The final sections of the Chapter describe the catalysts and analytical techniques used during the course of the research. Chapter 3: Continuous Hydrogenation in Supereritical Fluids This Chapter opens with a summary of some initial hydrogenation work carried out at Nottingham prior to this research. The results section reports a range of non-selective hydrogenation reactions, commencing with a detailed study of the hydrogenation of cyclohexene which was used to explore the capabilities of the equipment. Chapter 4: Continuous Selective Hydrogenation in Supercritical Fluids This Chapter is a continuation of Chapter 3 and begins with an introduction to different types of selective hydrogenation, then highlights some literature examples of selective hydrogenations conducted in supercritical fluids. The results section reports several selective hydrogenation reactions conducted at Nottingham. Chapter 5: Continuous Friedel-Crafts Alkylation and Acylation Reactions This Chapter begins with a discussion of the problems associated with conventional Friedel-Crafts chemistry, most of which are associated with the homogeneous catalysts normally used. A review of the use of various solid acid materials investigated for Friedel-Crafts type activity follows and this section concludes with literature examples of some supercritical Friedel-Crafts processes. The results section begins by reporting Friedel-Crafts alkylation reactions and closes with a brief amount ofFriedel-Crafts acylation.