aula e apresentação do curso de catalise heterogenea

catalise

1. Preparation of heterogeneous
catalyst
lec11 week 14

2. •Industrial catalysts are generally
shaped bodies of various forms, e.
g., rings, spheres, tablets, pellets.
•The production of heterogeneous
catalysts consists of numerous
physical and chemical steps.
•The conditions in each step have a
decisive influence on the catalyst
properties.
•the main physical properties of a
catalyst that are influenced by the
production Conditions are: Active
surface area; pore structure;
mechanical strength.

3. Components of a Typical
Heterogeneous CatalystA. Active phase - metal that provides active sites where the
chemical reaction takes place
B. Support or Carrier - high surface area oxide which
disperses and stabilizes the active phase
(adds efficiency, physical strength, sometimes selectivity)
C. Promoter(s) - additive which improves catalyst properties,
e.g. activity, selectivity, catalyst life

4. Bulk catalysts
•Bulk catalysts also known as
precipitated catalysts are
mainly produced when the
active components are cheap.
•The preferred method of
production is precipitation.
•One or more components in
the form of aqueous solutions
are mixed and then co
precipitated as hydroxides or
carbonates. An amorphous or
crystalline precipitate or a gel
is obtained, which is washed
thoroughly until salt free. This
is then followed by further
steps: drying, shaping,
calcination, and activation

5. Preparation of bulk catalyst

6. Typical examples of precipitated catalysts
are:

7. Impregnated catalyst ( support catayst)
•One of the best known methods for producing
catalysts is the impregnation of porous
support materials with solutions of active
components.
•Especially catalysts with expensive active
components such as noble metals are
employed as supported catalysts.
•A widely used support is Al2O3, Activated
carbon and silica gel.

8. Preparation of catalyst by
impregnation
•Impregnation as a means of supported catalyst
preparation is achieved by filling the pores of a
support with a solution of the metal salt.
•The catalyst is prepared either by spraying the
support with a solution of the metal compound
or by adding the support material to a solution of
a suitable metal salt, This is then followed by
drying and subsequent decomposition of the salt
at an elevated temperature, either by thermal
decomposition or reduction.

9. impregnation
•The support is immersed in
a solution of the active
component under precisely
defined conditions
(concentration, mixing,
temperature, time).
Depending on the
production conditions,
selective adsorption of the
active component occurs on
the surface or in the interior
of the support. The result is
non uniform distribution.

10. Supported metal catalyst

13. The advantages of impregnated catalysts
compared with precipitated catalysts
•Pore structure and surface of the catalyst can
be controlled.
•More economic, since the content of
expensive active components is often low.
•The distribution and crystallite size of the
active components can generally be varied
over a wide range.
•Multiple impregnation is possible.

14. Examples of industrial impregnated
catalysts are:
–Ethylene oxide catalysts in which a solution of a
silver salt is applied to Al2O3
–Catalysts in the primary reformer of ammonia
synthesis, with 10–20 % Ni on Al2O3
–Catalysts for the synthesis of vinyl chloride from
acetylene and HCl: HgCl2/activated carbon; HgCl2
is applied from aqueous solution

15. Dry mixing
•Physically mixed, grind, and calcination