The physical state of the catalyst, including its particle size, surface area, and porosity, significantly affects its activity and selectivity. For instance, a higher surface area provides more active sites for the reaction, while optimal porosity ensures efficient mass transfer of reactants and products. Techniques such as [X-ray diffraction (XRD)](https://) and [scanning electron microscopy (SEM)](https://) are commonly used to characterize and control the physical properties of catalysts.
