In-situ titrations employed in the estimation of active site densities oftentimes only provide upper bound estimates, not true active site densities. Discounting unselective contributions that result in a disparity between the two requires a treatment of transient titration data more nuanced than merely integrating under the titrant breakthrough curve. Three methods for estimating site densities (and turnover frequencies) are presented in the context of ceria-catalyzed ethene hydrogenation, and their strengths and limitations discussed. Readily accessible supra-monolayer coverages of CO prevalent on ceria surfaces help bring into relief considerations relating to unselective adsorption and active site heterogeneity common, yet infrequently addressed, in the characterization of heterogeneous catalysts using in-situ titration methods.

用于估计活性位点密度的原位滴定通常只提供上限估计值，而不是真实的活性位点密度。消除导致两者之间差异的非选择性贡献需要对瞬态滴定数据进行更细致的处理，而不仅仅是在滴定剂突破曲线下积分。在二氧化铈催化乙烯氢化的背景下，提出了三种估计位点密度（和周转频率）的方法，并讨论了它们的优势和局限性。在二氧化铈表面上普遍存在的易于获得的超单层 CO 覆盖有助于缓解与非选择性吸附和活性位点异质性相关的问题，这些问题在使用原位滴定法表征非均相催化剂时很常见，但很少得到解决。