Catalysts

Catalysts are substances that change the rate of a chemical reaction and are not part of the final products.

Catalysts provide energetically less hindered reaction pathways that allow efficient use of raw materials.
Catalysis is the acceleration of chemical reactions by the action of small quantities of substances (catalysts) that do not themselves change during the reaction.
It is widely used in refining petroleum, obtaining various products and creating new materials (e.g. plastics).
Approximately 90% of modern chemical production is based on catalytic processes.
Catalysts make it possible to turn low-grade raw materials into high-value products.
Without catalysts, it would not be possible to produce motor fuels for Euro 5 or higher engines.
For example, in catalytic cracking, one of the key processes for increasing the yield of light products (especially gasoline), the most important catalyst action is to break down large hydrocarbon molecules into smaller ones with a higher octane number.

Hydrocracking in turn is the process of producing high quality paraffin and diesel distillates from vacuum distillation heavy gas oils and secondary processes.
It also produces a high quality base oil base that is close to synthetic oil in terms of performance.
In other words, it is catalytic cracking in the presence of hydrogen - where the combination of hydrogen, a catalyst and the appropriate process regime can crack low-quality light gas oil and produce high-quality bases for a wide range of commercial lubricating oils.
The catalysts play an important role in this process: they actively interact with hydrogen, they ensure that the cracking itself takes place and that isoparaffins are formed.

Hydrotreating is the most large-scale catalytic process in refining.
Hydrotreating reduces the sulphur content of the fuel.
The efficiency of hydrotreating depends on catalyst activity, temperature regime and feedstock quality.
And increasing the efficiency of the process requires the use of new types of catalyst. 

Requirements for catalysts:

•     constant high catalytic activity,
•     selectivity,
•     mechanical strength,
•     temperature resistance,
•     resistant to catalytic poisons,
•     long service life,
•     easy regenerability,
•     necessary hydrodynamic characteristics,
•     low cost.

 The activity is determined by the reaction rate per unit volume or mass of the catalyst and depends on its chemical composition.
The formation of catalyst properties takes place during its preparation and during operation, so the catalyst preparation method must take into account the possibility of the formation of active centres under catalytic conditions. In many cases, the activity of industrial catalysts is increased by adding promoters (co-catalysts).

The selectivity changes due to changes in the electronic properties and surroundings of the active centres of the catalyst (ligand effect).
In reactions of complex organic molecules, of great importance is the preferential formation of a product that is close in shape and size to the catalyst micropore.
In complicated multi-stage reactions multiphase multicomponent catalysts are used; their selectivity is higher due to the fact that each stage of a complex reaction is accelerated by a different component of the catalyst. The selectivity of a catalyst also depends on its porosity, grain size and the nature of its stacking.

The thermal stability of catalysts is important for the first reactant layers in exothermic reactions where heat release can cause recrystallisation and deactivation of the catalysts.
To prevent recrystallisation, catalysts are deposited on heat resistant carriers.

The resistance of a catalyst to the action of catalytic poisons is determined by the specifics of their interaction with the catalyst.
Metallic catalysts are poisoned by compounds of oxygen (H2O, CO), sulphur (H2S, CS2, etc.), N, P, As and other substances that form a stronger chemical bond with the catalyst than the reacting substances.
Oxide catalysts are affected by the same poisons, but oxides are more resistant to poisoning.
In cracking, reforming and other hydrocarbon reactions, catalysts are poisoned by covering them with a layer of coke.
In addition, catalysts can also be deactivated by mechanical coating of the surface with dust that is introduced from outside or formed during catalysis.

Catalyst preparation

Catalysts with a developed specific surface area are widespread method of precipitation from aqueous salt solutions followed by calcination of the resulting compounds.
Many metal oxides are produced in this way. In this case, it is better to use aqueous NH3 solution, as there is no need to wash the precipitate from alkali metals.
The cooled catalyst is crushed, sieved and reduced with a nitrogen-hydrogen mixture in a synthesis column.
Special shaping machines are used to obtain the correct geometric shape of the catalyst grains.
Cylindrical granules are obtained by extruding (squeezing) the wet mass through holes of the required diameter using a massive screw, after which the obtained bundle is cut into individual cylinders which are
The obtained bundle is then cut into individual cylinders which are rolled into spherical pellets in special granulators.
Flat cylindrical pellets are produced by pressing dry powder on tabletting machines