Abstract
Practical catalysts with a porous framework, such as zeolites, host catalytic reactions at active sites engrained in the pores and channels of the scaffold. The mechanism of interaction at these active sites, defining catalyst performance, remains elusive, in large part, due to the lack of surface characterization methods available for thick films or powders. Here, we present thin film analogs of practical catalysts that allow for the implementation of surface characterization tools, including advanced microscopy and operando spectroscopy methodologies. Specifically, we investigated bilayer silica, MFI nanosheets, and UiO-66 thin films using a multi-modal approach addressing film growth, characterization, and gas adsorption aimed at understanding catalytic activity, reactivity, and selectivity properties, as defined by molecular-level changes in the reaction mechanism.
Highlights
The surface science approach to study catalysis begins with a simplified model of a practical catalyst and builds on this scheme with increasing complexity to bridge the “materials gap.”1 For example, initial investigations can involve well-defined single crystalline metal surfaces followed by oxide thin films and supported nanostructures, which mimic the material complexity of a practical catalyst
In the case of CO permeating a bilayer silica film to bind with a Pd(111) support, IR reflectionabsorption spectroscopy (IRRAS) data show the scitation.org/journal/adv adsorption geometry, while XPS data quantify the electronic interaction of the bilayer film after CO adsorption
The catalytic performance of many chemical reactions in zeolites is based on the acid strength and density of active sites in the microporous material; analogously, metal–organic frameworks (MOFs) are thought to have the same physical properties
Summary
The surface science approach to study catalysis begins with a simplified model of a practical catalyst and builds on this scheme with increasing complexity to bridge the “materials gap.” For example, initial investigations can involve well-defined single crystalline metal surfaces followed by oxide thin films and supported nanostructures, which mimic the material complexity of a practical catalyst. A fundamental science approach to uncover structure–property relationships in heterogeneous catalysis reactions at complex surfaces and interfaces is critical to understand and, control catalyst performance through the rational design of catalysts This goal requires advanced multi-modal operando characterization methods to capture changes in surface structure and chemistry of the catalyst under conditions relevant to applications. Photoemission spectroscopy is a complementary technique with additional element- and orbital-specificity to identify active site oxidation states and reaction intermediates in addition to quantifying reaction components.17,20 Such vibrational and electronic measurements are relevant to porous materials. Research investigations implementing a multi-modal approach using microscopy and spectroscopy techniques under UHV and operando conditions are routinely performed on individual instruments.
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