Abstract
Catalysis is an indispensable part of our society, massively involved in numerous energy and environmental applications. Although, noble metals (NMs)-based catalysts are routinely employed in catalysis, their limited resources and high cost hinder the widespread practical application. In this regard, the development of NMs-free metal oxides (MOs) with improved catalytic activity, selectivity and durability is currently one of the main research pillars in the area of heterogeneous catalysis. The present review, involving our recent efforts in the field, aims to provide the latest advances—mainly in the last 10 years—on the rational design of MOs, i.e., the general optimization framework followed to fine-tune non-precious metal oxide sites and their surrounding environment by means of appropriate synthetic and promotional/modification routes, exemplified by CuOx/CeO2 binary system. The fine-tuning of size, shape and electronic/chemical state (e.g., through advanced synthetic routes, special pretreatment protocols, alkali promotion, chemical/structural modification by reduced graphene oxide (rGO)) can exert a profound influence not only to the reactivity of metal sites in its own right, but also to metal-support interfacial activity, offering highly active and stable materials for real-life energy and environmental applications. The main implications of size-, shape- and electronic/chemical-adjustment on the catalytic performance of CuOx/CeO2 binary system during some of the most relevant applications in heterogeneous catalysis, such as CO oxidation, N2O decomposition, preferential oxidation of CO (CO-PROX), water gas shift reaction (WGSR), and CO2 hydrogenation to value-added products, are thoroughly discussed. It is clearly revealed that the rational design and tailoring of NMs-free metal oxides can lead to extremely active composites, with comparable or even superior reactivity than that of NMs-based catalysts. The obtained conclusions could provide rationales and design principles towards the development of cost-effective, highly active NMs-free MOs, paving also the way for the decrease of noble metals content in NMs-based catalysts.
Highlights
The fast growth rate of population in the last decades has led to an unprecedented increase in energy demands
It is well established today—thanks to the rapid development of sophisticated characterization techniques—that various interrelated factors, such as the composition, the size, the shape, and the electronic state of metal oxides (MOs) different counterparts can exert a profound influence on the local surface chemistry and metal-support interactions, and in turn, on the catalytic activity of these multifunctional materials [6,48,51,52,62,63,64,65,66,67,68,69,70,71,72,73,74]
An almost linear relationship is revealed between the redox properties, expressed either as Os/Ob or ID/IF2g ratio, and the CO oxidation performance, in terms of half-conversion temperature (T50), of ceria nanoparticles (Figure 7c), clearly demonstrating the implications of shape modulation in catalysis
Summary
The fast growth rate of population in the last decades has led to an unprecedented increase in energy demands. It is well established today—thanks to the rapid development of sophisticated characterization techniques—that various interrelated factors, such as the composition, the size, the shape, and the electronic state of MOs different counterparts can exert a profound influence on the local surface chemistry and metal-support interactions, and in turn, on the catalytic activity of these multifunctional materials [6,48,51,52,62,63,64,65,66,67,68,69,70,71,72,73,74]. IInn tthheeffoolllloowwiinngg,,tthheebbaassicicpprrininccipiplelessoof fsisziez,es, hshapape,ea, nadndeleelcetcrtornoinc/icch/cehmemicaiclaelffeefcftescatsrearperopvriodveiddeind sinepsaerpaatreasteecsteioctniso.nIst. sIht sohuoldulbdebsetrsetsrseesdse, dh,ohwoewveevr,etrh, atht atht itshdisisdtirsitcrticptrpesreensetanttiaotniodnodeosensontoatlsaolsmo meaenaan daisdtirsitcrticetffeefcfteoctf eoafcehacfahctfoacrtionrciantaclaytsailsy.sAisl.mAolmst oasllt paallrapmareatmerestaerres ianrteerinretleartreedla; ttehdu;st,hthues,dtihsecrdeitsecrroeltee orof leeaochf eoanceh ionntehienctahtealcyattiaclyactitcivaicttyivoiftyMoOf Ms cOansncoant nbeotebaesielyasdiliyscdloissceldo,saeds ,fuasrtfhuerrthdeirscduisssceudssbeedlobwel.ow
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