Heterogeneous implies that something is not uniform in nature and contains a few or many different components, or substances that make up one whole or mixture. In chemistry, it can also mean something is comprised of the same substance only in different phases (gas, liquid, solid). For example, ice water is heterogeneous because it is comprised of liquid water and solid water. In sustainability, heterogeneity can confer some desirable properties. In consideration of a catalyst, heterogeneous catalysts confer many advantages compared to homogeneous catalyst including better stability, ease of handling, separation, and simplified recycling of the catalyst.