Fast visual evaluation of the catalytic activity of CeO2: Simple colorimetric assay using 3,3′,5,5′-tetramethylbenzidine as indicator

Abstract

Evaluation of the catalytic performance of CeO2 typically requires dedicated (GC or MS) analysis over extended times. Herein, we present a simpler and fast method of assessing the catalytic activity of CeO2 through 3,3′,5,5′-tetramethylbenzidine (TMB) color change. Five different morphologies (nanoflakes (NF), nanorods (NR), nanoparticles (NP), nanocubes (NC) and nano-octahedra (NO)) of CeO2 were used as test models, and their catalytic activity can be rapidly predicted within 10 min by the developed TMB method. Depending on the CeO2 catalytic activity, which is related to O2 dissociation under strongly acidic conditions (0.05 M H2SO4, pH = 1), more or less of highly reactive hydroxyl species are produced, which can subsequently oxidize TMB from colorless to yellow. This change can be observed even by the naked eye or, preferentially, by a UV–vis spectrometer. The feasibility of the TMB-H+ system to assess catalytic activity was verified by the imine synthesis, methylene blue degradation and CO oxidation. The TMB method can thus rapidly and accurately indicate the catalytic activity of CeO2 with different morphologies, and can be used for pre-screening of synthesized materials, avoiding time-consuming and/or more complex characterization of CeO2 samples with poor catalytic activity.