Acids not only include the well-known liquid acids, such as sulfuric acid, hydrochloric acid, and nitric acid, but also include acids in the solid state such as activated clay, synthetic molecular sieves, and supported acids, collectively referred to as solid acids. Compared to liquid acids, solid acids have many advantages, such as producing less waste liquid in catalytic reactions, posing less harm to human health and equipment, and avoiding difficulties in separating catalysts and products (Yu and Liu 2006). Therefore, the industrial application of solid acids, especially as catalysts, is becoming increasingly widespread.