Difference Between Hydrogenation and Reduction

The key difference between hydrogenation and reduction is that hydrogenation requires a catalyst whereas reduction does not require a catalyst unless it is hydrogenation. Hydrogenation is a form of reduction reaction in which molecular hydrogen combines with an existing molecule. Therefore, hydrogenation and reduction relate each other.

A reduction can be a decrease of oxidation number, loss of oxygen or addition of hydrogen. But some reduction reactions do not involve either oxygen or hydrogen as reactants. Therefore, the most acceptable definition for reduction is a decrease of oxidation number. In addition to the above key difference, there are some other differences between these two chemical reactions such as the components of the chemical reaction; molecules having double or triple bonds can undergo hydrogenation while any molecule having atoms with higher oxidation numbers can undergo reduction reactions.

CONTENTS

1. Overview and Key Difference
2. What is Hydrogenation
3. What is Reduction
4. Side by Side Comparison – Hydrogenation vs Reduction in Tabular Form
5. Summary

What is Hydrogenation?

Hydrogenation is a chemical reaction that includes the addition of molecular hydrogen to a chemical species. Furthermore, this reaction usually takes place in the presence of a catalyst; nickel, palladium, platinum or their oxides. It is helpful to either reduce or saturate a chemical compound. Hydrogenation can affect a molecule in two ways;

1. Saturation of a compound containing either double or triple bonds
2. Dissociation of a molecule

Almost all the unsaturated compounds are capable of reacting with molecular hydrogen.

This chemical reaction is useful in many industrial purposes for the synthesis of different compounds such as hydrogenation is useful in petroleum industry for the production of different petrochemicals.

What is Reduction?

Reduction is the decrease of oxidation number of a chemical species. This reaction is a half reaction of a redox reaction (a redox reaction has two chemical reactions that occur parallel to each other; oxidation and reduction). A reduction reaction decreases the oxidation number while oxidation reaction increases the oxidation number.

Sometimes, reduction is the removal of oxygen or addition of hydrogen to a chemical species. Moreover, this type of reaction occurs in three main ways; decrease the oxidation number from a positive value to a negative value, from zero to negative value or from negative to further negative value. A common example for a reduction reaction is the decrease of the oxidation number of Copper (II) to copper (0).

What is the Difference Between Hydrogenation and Reduction?

Hydrogenation is a chemical reaction which includes the addition of molecular hydrogen to a chemical species. Reduction is the decrease of oxidation number of a chemical species. Hydrogenation and reduction reactions relate to each other because hydrogenation is a form of reduction.

However, there are some differences between these two chemical processes as given below. For example, hydrogenation essentially requires a catalyst for the progression of the reaction while reduction does not require a catalyst unless it is hydrogenation. And also, hydrogenation occurs with unsaturated molecules while reduction occurs with any chemical species having a higher oxidation number.

Summary – Hydrogenation vs Reduction

Hydrogenation and reduction are important chemical reactions that have many applications in industries. Hydrogenation is a form of reduction. The difference between hydrogenation and reduction is that hydrogenation requires a catalyst whereas reduction does not require a catalyst unless it is hydrogenation.

Reference:

1. Helmenstine, Anne Marie, Ph.D. “Reduction Definition in Chemistry.” ThoughtCo, Sep. 3, 2017. Available here 
2. “Hydrogenation.” Wikipedia, Wikimedia Foundation, 25 May 2018. Available here  

Image Courtesy:

1.’Alkene to alkane’By Robert at English Wikibooks (Public Domain) via Commons Wikimedia  
2.’Chelidonic acid reduction’By Hbf878 – Own work, (CC0) via Commons Wikimedia