Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Noble metal-free CeO 2 -based mixed oxides for CO and soot oxidation Deboshree Mukherjee a,b , Benjaram M. Reddy a,b, ⁎ a Inorganic and Physical Chemistry Division, CSIR – Indian Institute of Chemical Technology,Uppal Road, Hyderabad 500 007, India b Academy of Scientiﬁc and Innovative Research, CSIR-Indian Institute of Chemical Technology, Hyderabad, India ARTICLE INFO Keywords: Doped CeO 2 Dopant inﬂuence Relative oxygen vacancy Oxygen storage/release capacity Surface defect concentration ABSTRACT ‘Three-way catalytic technology’ has been successfully implemented in automobile industries for cleaning of auto exhaust gases from 1980’s onward. Supported noble metal catalysts with ceria (CeO 2 ) as the redox promoter have been employed for this technology. However, these catalytic materials have some drawbacks in terms of high light oﬀ temperature, catalyst poisoning and drop of activity, heavy metal pollution, etc. Hence, this technology is under active investigation throughout for the sake of better performance. Considerable research eﬀorts have been devoted to develop new advanced materials. Noble metal-free CeO 2 -based mixed oxides, which can be deployed as potential substitutes, have been investigated at length with the goal to overcome the lim- itations like loss of stability and activity at elevated temperatures, improvement of oxygen storage/release ca- pacity (OSC), and so on. However, the use of proper dopants at optimum concentration and tuning of the shapes, size and morphology of the nanoparticles via controlled synthesis is a challenging task, since it improves the features of CeO 2 . In this article, we have reviewed the inﬂuence of these factors on the properties of ceria-based materials and their catalytic eﬃciencies in CO and soot oxidation reactions. 1. Introduction Ceria (CeO 2 )-based materials have been investigated at length both in industry and academia and successfully implemented for a variety of technical applications in recent past, one of which with vital im- portance is elimination of toxic automobile exhaust pollutants [1,2]. Automobile exhaust contains diﬀerent ratios of hazardous compounds including carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbon (UHC), particulate matters (PM), etc., generated during incomplete combustion of fossil fuel in internal combustion engine [3]. From 1980 onwards, the three-way-catalytic convertor (TWC), com- prised of supported noble metal (NM) and CeO 2 as a vital redox pro- moter is in use for mitigation of the harmful eﬀects of exhaust gas. CeO 2 has the ability to store and release oxygen depending on the sur- rounding O 2 partial pressure. Under oxygen-rich condition of the ex- haust gas atmosphere, CeO 2 absorbs oxygen and helps in the reduction of NO X to N 2 . On the other hand, in oxygen deﬁcient condition, CeO 2 releases the stored oxygen to carry out the oxidation of CO and UHC to relatively harmless CO 2 and water vapor [4]. Thus, optimal eﬃciency of the operating catalyst is attended, when the air and fuel mixture in the engine is periodically altered from slightly rich in oxygen to slightly poor in oxygen. Distinct technical advances have been brought about till the in- troduction of the ﬁrst catalytic convertor. Despite, signiﬁcant research and development activity is prevailing both in industry and academia with three major goals; ﬁrst, meeting the ever tightening emission standards, which require continued catalytic activity, durability, and improved selectivity [5]. Second, attending 90% conversion of the ex- haust gas pollutants within 423 K temperature or even lower, without increasing the production cost. Thus, minimization of the waste heat generation will also help enhance of the engine eﬃciency [6]. Third, ﬁnding an alternate of the expensive Pt group metals (PGM), used to promote the oxidation reactions in the modern catalytic convertor [7]. The compounds of PGM are hazardous to health and environment, whereas, Pd and Rh are carcinogenic in nature. Contamination of these PGM compounds from the scrap of automobile catalyst wash-coat is a signiﬁcant cause of heavy metal pollution. Other than that, failure of catalytic convertor may also takes place due to few factors including melting down of the catalytic convertor, carbon deposit, catalyst frac- ture, poisoning, etc., which have been addressed in detail in the lit- erature [8]. A wide range of new materials is under investigation, in- cluding perovskite and delafossite materials, to reach these goals [9]. However, another potential option is to bring down the working tem- perature of CeO 2 without using noble metals. The redox catalytic ability and structural stability of CeO 2 can be manipulated in various ways. Introduction of foreign cations in the crystal lattice of CeO 2 , shape and size controlled synthesis of the CeO 2 nanoparticles, use of proper carrier materials are few among them. In the literature several studies have http://dx.doi.org/10.1016/j.cattod.2017.06.017 Received 10 April 2017; Received in revised form 8 June 2017; Accepted 19 June 2017 ⁎ Corresponding author at: Inorganic and Physical Chemistry Division, CSIR – Indian Institute of Chemical Technology,Uppal Road, Hyderabad 500 007, India. E-mail addresses: bmreddy@iict.res.in, mreddyb@yahoo.com (B.M. Reddy). Catalysis Today xxx (xxxx) xxx–xxx 0920-5861/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Mukherjee, D., Catalysis Today (2017), http://dx.doi.org/10.1016/j.cattod.2017.06.017