الفهرس 
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Abstract
Catalysis and Catalysts
Berzelius defined catalysis in 18361 when he wrote ”many bodies have the property of exerting on other bodies an action which is very different from chemical affinity.
By means of this action they produce decomposition in bodies and fonn new compounds into the composition of which they do not enter. This new power, hitherto unknown, is cornman both in organic and inorganic nature I shall call it catalytic power. I shall
also call catalysis the decomposition by this force”. A more recent definition given by Bond2 emphasises the point that equilibrium is reached more rapidly in the presence of
a catalyst than in its absence. Another point he makes is that catalysts can control
the direction of the reaction.
Catalysis falls into two groups, homogenous catalysis, where reactants and catalyst are in the same phase, and heterogenous catalysis, where they are in different phases. This work will concentrate on the latter, in particular, systems with gas-phase reactants and solid catalysts. The most commonly studied heterogenous catalysts are metals, oxides and sulphides.
The metals with greatest catalyic activity are those in the d-block, almost all
can chemisorb oxgyen, all of them can chemisorb hydrogen, ethyne, ethene and carbon monoxide3. This makes metals good catalysts for reactions involving hydrogen(e.g. hydrogenation, dehydrogenation and hydrogenolysis).
The use of a support is very common. Dispersing the catalytically active material on a support of high surface area leads to the productions of small particles, yielding an active phase with a higher surface area for a given weight that could be obtained by any other method. Satterfield(4) lists the criteria which should be satisfied by a practical support:
1- Inertness
2- Mechanical strength