Propylene
is an important chemical used in the production of polypropylene,
propylene oxide, propylene carbonate, and many more useful chemical
compounds. High propylene demand and low industrial production motivate
propane dehydrogenation (PDH) technology for propylene production.
CrO
x
and Pt–Sn catalysts are employed
for industrial PDH, occurring via the nonoxidative route. Cr-based
catalysts face serious health and environmental issues. Moreover,
the nonoxidative route used industrially faces thermodynamic limitations
and catalyst deactivation occurring, because of recrystallization,
sintering, agglomeration, and coking. The nonoxidative routes favor
homolytic dissociation of the bonds (because of positive values of
ΔG and ΔH of reaction),
while both homolytic and heterolytic dissociation are observed in
the oxidative route. Nonoxidative PDH follows the Langmuir–Hinshelwood
mechanism, whereas oxidative PDH can occur via the Langmuir–Hinshelwood
mechanism (with soft oxidants such as CO2, S2, SO2, and NO
x
) or the Mars–van
Krevelen mechanism (with O2). First-order kinetics of nonoxidative
PDH and cracking is observed at low partial pressures of propane,
whereas, at high partial pressures, it becomes zero-order, along with
standard Gibbs free energy of the reaction (ΔG
R
0) and enthalpy change of the reaction (ΔH
R
0) equal to 86.2 kJ mol–1 and 124.3 kJ mol–1, respectively, at 25 °C. ΔG
R
0 values for all the steps of oxidative PDH are negative, showing
the thermodynamic feasibility of the oxidative route for PDH. Using
H2 as a cofeed for nonoxidative PDH removes the precursor
of coke, which increases catalyst stability and decreases the coke
formation rate. Water addition results in an increase in the COx selectivity
with an increment in the amount of water. The effect of promoters,
reaction conditions, and support on Pt and Pt-based catalysts in terms
of selectivity and yield of propylene, conversion of propane, changes
in binding and bond dissociation energies, and activation energy is
discussed with the help of DFT calculations and characterization techniques,
such as X-ray photoelectron spectroscopy (XPS), extended X-ray absorption
fine structure (EXAFS), etc. Limitations of coking and regeneration
cycles and possible theoretical improvements through mathematical
calculations and simulations are discussed for further research in
PDH.