Berzelius first used the word catalysis in 1835, to summarise the effect on a variety of reactions of the addition of a substance which was able to spped up the reactions but itself remain chemically unchanged. Nowadays a catalyst is better defined as "a substance which will alter the rate of a chemical reaction, itself remaining chemically unchanged at the end of the reaction". Whilst catalyst are now in everyday use particularly in process industries, much is still unknown about how they actually work. Therefore most scientists still consider the field of catalysis to be a 'black science".
There are 2 main ways in which a catalyst may interact with reactant particles to provide a pathway with lower activation energy. The first is HETEROGENEOUS CATALYSIS, in which the catalyst and reactant are in different phases - physically distinct such as a metal catalyst working in a liquid or gas stream. The second is the HOMOGENEOUS CATALYSIS, in which the catalyst is in the same phase as the reactant - where the whole reaction mixture has a uniform composition.
Henry Broquet's development of the fuel catalyst in 1941 while stationed with the RAF in Murmansk, owes much to the prior knowledge and experience with tin catalysis, of the Russian scientists in his team. In the 1940s metal catalysts were also beginning to be widely used for coal liquifaction and petroleum refining processes. It was found that the metal catalyst could be used to control the speed and result of breakdown reactions of coal and petroleum products. Tin, which is one of the constituents of Broquet, featured quite prominently in this work and the use of a tinplate grid as a catalyst was patented for the first UK coal liquifaction plant. Today tin, and other metals, are commonly used as catalysts with many hydrocarbons including fuels, oils, and plastics.
The Broquet metal pellet, better known as the Broquet fuel catalyst, acts as heterogeneous catalyst when immersed in hydrocarbon fuels. With Broquet in solid metal form, and the reactant being hydrocarbon fuel in liquid form. Only the catalyst surface is in contact with the reaction mixture and as the catalyst increases the activated fraction, the collisions between reactant molecules require less energy than normal. In general, reactant molecules are absorbed onto the catalyst surface (not absorbed into the catalyst). In this process reactant molecules stick to the catalyst by forming weak chemical bonds. This chemisorption weaken the bonds within the reactant molecules. The absorbed reactant molecules are now much more susceptible to reaction. They are still able to move over the catalyst surface and products are formed when they collide. In addition, the absorbtion process effectively concentrates the reactant molecules on the catalyst surface, increasing the total collision frequency. The final, and important step, is desorption where the product molecules leave the catalyst surface. When this occurs, the catalyst surface will then be available to absorb fresh reactant molecules. The efficiency of such a catalyst will depend upon how strongly it absorbs reactant molecules. Up to a certain point catalytic activity increases as the strength of absorbtion increases, since the bonds within the reactant molecules are further weakened. As the catalyst is, by definition, not used up in the process, only a small amount of catalyst material is necessary to give the required results. In the case of the Broquet fule catalyst, an active life of 250,000 miles (400,000kms) or 6,500 hours for boats, generators, oil-fired boilers and off-road applications, would be expected.
With regard to the combustion process (in itself a partially unknown process), the idea of chemically modifying this by influencing the rates of reaction is not new. Initiator substances are common fuel additives. Propagation and branching control by additives including tetraethyl lead are well known, but again not totally understood. The combustion of fuel itself involves a complex series of chemical and physical steps, energy being released as fuel components are progressively fragmented into smaller and less complex molecules. During the peak stages of these process, carbon monoxide is being formed at near infinitely fast rates. Because the terminal oxidation of carbon monoxide to carbon dioxide is not a simple reaction (even with excess air) the combustion environment in a diesel engine, for example, at this pointtends to become saturated with CO. This saturated state restrains the natural progression and rate of combustion, reduces efficiency and leads to the formation of undesirable reaction products, including soot.
The effects of Broquet on such hydrocarbon fuels as petrol, diesel and oil, is that of combating the detrimental effects of fuel storage, oxidation of unsaturated hydrocarbons, and dissolved trace metals.
It is widely recognised that dissolved trace metals occur in all fuels and oils and it has been established that these trace amounts will promote various oxidative processes in organic systams. While it has been observed that iron, zinc and lead can promote oxidative degradation of hydrocarbon fuels (Schenk 1971), copper and its compounds have been shown to comprose the most active instability promoters (Pederson 1949; Smith 1967). Trace amounts of copper are commonly found in fuels, introduced during the copper - sweetening process or from the contact of refinery streams with copper line, brass fittings, admiralty metal and other copper - bearing alloys. Copper concentrates as low as 0.1 ppm have been shown to exert a marked effect on fuel stability (Barusch & MacPherson 1965). Other metals are either naturally occuring contaminates, or have been picked up during the transportation and storage phases caused by the action of organic acids and other organic molecules. These metal can act as catalysts, which initiate breakdown reactions in the presence of oxygen, either in storage, or combustion to form sludges, cokes and gums. Modern fuels and oils company commonly employ Metal Deactivating Agents (MDA's) as one approach to reduce the catalytic activity of dissolved metals. The findings from accelerated stability tests have indicated that MDA's can enhance thermal stability to varying degrees resulting in the formation of deposits during the combustion process. In addition, the MDA's reduce the rate of oxygen consumption with commensurate reductions in hydroperoxide concentrations.
The trace metal compounds are often present as 'metal soaps' (napthenates) or metal atoms linked to long organic acid molecules, which hold them in solution. By the use of the Broquet fuel catalyst, they can change from this soluble and active form to an insoluble and in active form by reacting with water (hydrolyse), or possible redox reactions (electronic interchanges). Even in storage, fuel will deteriorate, due to evaporation, oxidation again, and micro-organism growth and corrosion. Therefore the Broquet effect is again very important in not only deactivating or passivating metals and retarding the oxidative degradation reactions, but also in the same step, converting the metals to oxides which can be oxidation catalysts and aid combustion.
The overall effect of the Broquet fuel catalyst when applied to the fuel system of any engine running on a hydrocarbon-based fuel is to propagate a quicker and more stable flame front. This enables more of the fuel mixture in the combustion chamber to be usefully burned and therefore less wasted down the exhaust pipe or converted to carbon deposits, waxes or gums. The benefits to the driver, or operator, of the vehicle is an increase in power, or better economy ( this will depend upon how the additional energy is utilised, i.e. whether to carry more load, travel faster, or to drive in an identical manner as previously and gain the fuel economy), reduced exhaust emissions, cleaner combustion zones and components.
Whilst more dramatic improvements are noticeable when Broquet is fitted to older engines, due in part to the 'cleaning' effect of Broquet on combustion zones and components. Broquet should ideally be fitted to a fuel system of an engine when new. In doing this the engine is protected from the damage caused by poor combustion (e.g abrasive effects of carbon deposits), and the workload on catalytic converters (where fitted) is reduced due to the reduction of emissions (hydrocarbon, carbon monoxide and naturally occurring lead). Broquet forms an ideal and natural partnership with 'cats' in that by reducing emissions. The use of Broquet can extend the working life of the 'cat' and also ensures that emissions from the engine are reduced the moment the engine is started. This allows the 'cat' time to reach its full operating temperature, without becoming a 'polluter'.