Differences between Homogeneous Catalysis and Heterogeneous Catalysis

Homogeneous catalysis takes place when the catalyst and the other reactants are all dissolved in the same solution. Heterogeneous catalysis typically involves the use of a catalyst that is insoluble, or perhaps only weakly soluble, in the solution in which the reaction takes place. Thus, in heterogeneous catalysis, the catalyst and solution may form a suspension, or the catalyst may simply be a solid that is placed in the solution.

Differences between Homogeneous Catalysis and Heterogeneous Catalysis are mentioned below:

Homogeneous catalysis

• Homogeneous catalysts are catalytic compounds that are in a similar phase as the substances which are going into the reaction phase.
• These types of catalysts usually are common in either the liquid phase or gas phase
• Operative temperature for homogeneous catalysis is generally low except only when under high pressure.
• The recovery of homogeneous catalysts is complicated and exclusive.
• The partition of homogeneous catalyst from the reaction mixture is complex.
• The heat transfer in homogeneous catalysis is very high as all the molecules of reactants and catalysts are in the same phase.
• Recycling methods are not very cost effective as it’s a long drawn process and as it’s a difficult treatment method for spent catalysts
• Modification of homogenous catalysts is very easy as it depends upon the tuning of electronic and steric properties on metal
• The recycling of homogeneous catalysts is not easy. The reaction mechanism is easier to find as varied techniques are available.
• The dynamic site of homogeneous catalysts is well-defined and has good selectivity.
• The thermal constancy of homogeneous catalysts is poor.

Homogeneous catalysts work better in low-temperature conditions (less than 250⁰C). In which the reactants and catalyst are in a similar phase. Example: 2SO₂(g) + O₂(g) —– No(g) → 2SO₃(g).

Heterogeneous catalysis

• Heterogeneous catalysts are catalytic compounds that are in a contradictory phase from that of the phase of the reaction combination.
• Heterogeneous catalysis is found in the liquid phase, gas phase, and solid phase.
• Operative temperature for heterogeneous catalysis is harsh as compared to the homogeneous process.
• The recovery of heterogeneous catalysts is simple and inexpensive.
• The severance of heterogeneous catalyst from the reaction combination is simple.
• The heat transfer is relatively low as compared to homogeneous catalysis as the reactant molecules and catalysts are in a different phase.
• These catalysts although require reactivating treatment process but still quite cost effective.
• The modification of heterogeneous catalysts is relatively difficult as the controlling methods of particle size, as well as the active size at a molecular level, is really difficult.
• The recycling of heterogeneous catalysts is simple. The reaction mechanism is difficult to fins as the techniques utilized as the product is scrutinized and not the catalysts.
• The dynamic site of heterogeneous catalysts is not well-defined and has deprived selectivity.
• The thermal constancy of heterogeneous catalysts is superior. The severance of the catalyst from the reaction combination is simple.

Heterogeneous catalysts work enhanced in high-temperature conditions (around 250 to 500⁰C). In which the reactants and catalyst phases differ from each other. Example: 2SO₂(g) + O₂(g) —– pt(s) → 2SO₃(g).