Best practices in the characterization of bulk catalyst properties

Bulk characterization of a solid provides us with a spatially-averaged description of its physical and chemical properties. These properties are not site-specific, but they are critical for categorizing materials and understanding their catalytic performance. Important bulk chemical properties include elemental composition, crystal structure, atomic coordination environment, and the oxidation states of elements comprising the catalyst. Significant physical properties include accessible surface area, pore volume, pore diameter, and particle size distributions that exist at the various length scales of catalysis. Each physicochemical property is sensitive to the conditions employed for catalyst synthesis, storage, pre-treatment, activation, and characterization. Thus, it is imperative that authors fully describe materials and methods in publications as this metadata provides context for observed phenomena and allows others to recreate the exact conditions that are essential for reproducibility. Such protocols are necessary for a meaningful interpretation of differences in catalyst performance observed across laboratories. This perspective article defines bulk characterization, provides guidance on bulk characterization methods, and emphasizes important considerations and best practices. Our aim is to build a more nuanced understanding of catalyst characterization. We hope that awareness and application of the principles outlined herein will improve rigor and reproducibility in catalysis science.