catalystsacids

Catalystsacids are catalytic species that promote chemical reactions through acidic functionality. They include Brønsted acids, which donate protons, and Lewis acids, which accept electron pairs. As catalysts, they accelerate transformations by stabilizing charged intermediates and lowering activation energy, while being regenerated at the end of the catalytic cycle.

Brønsted acid catalysts encompass mineral acids such as sulfuric acid (H2SO4) and phosphoric acid (H3PO4), as well as organic acids like p-toluenesulfonic acid (TsOH). Heterogeneous solid acids include sulfated zirconia, zeolites, and sulfonated carbon materials. Lewis acid catalysts include metal chlorides such as AlCl3 and FeCl3, and solid supports like Al2O3, TiO2, and ZrO2, which activate substrates by coordination to electron-rich sites or by accepting electron density.

Applications span a range of organic and industrial processes. They are widely used in esterification, alkylation, and hydration reactions; in polymerization, particularly cationic polymerization; and in biomass processing. In industry, solid acid catalysts underpin fluid catalytic cracking and refinery alkylation, while in fine chemicals they enable selective acylations and glycosylations. Acid catalysis is also employed in biodiesel production to esterify fatty acids with alcohols.

Advantages and challenges include high activity and selectivity under relatively mild conditions, countered by corrosivity, moisture sensitivity, or deactivation by coking and poisoning. Heterogeneous solid acids offer easier separation and reuse but may require regeneration to restore activity. Safety considerations involve handling corrosive acids and preventing equipment corrosion.

Research trends focus on recyclable solid acid catalysts with greater activity and stability, bifunctional Brønsted–Lewis systems, and the development of superacids for demanding transformations.