journal of traffic and transportation engineering (english edition) 2019; 6 (5): 419e440 Available online at www.sciencedirect.com ScienceDirect journal homepage: www.keaipublishing.com/jtte Review Article Application of hopcalite catalyst for controlling carbon monoxide emission at cold-start emission conditions Subhashish Dey a,*, Ganesh Chandra Dhal a, Devendra Mohan a, Ram Prasad b a Department of Civil Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India b Department of Chemical Engineering and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India highlights graphical abstract In the cold start period, the cata- lytic converter is entirely inactive, because the catalytic converter has not warmed up. The cold start phase is also depending upon the characteris- tics of vehicles. The amount of catalyst required to entrap the toxic pollutants throughout the cold-start period is usually much less than that needed in catalytic converters. Hopcalite (CuMnOx) catalyst could work very well at the low temper- ature, it can overcome the problem of cold-start emissions if used in a catalytic converter. article info abstract Article history: Carbon monoxide (CO) is a poisonous gas particularly to all leaving being present in the Received 19 March 2019 atmosphere. An estimate has shown that the vehicular exhaust contributes the largest Received in revised form source of CO pollution in developed countries. Due to the exponentially increasing number 12 June 2019 of automobile vehicles on roads, CO concentrations have reached an alarming level in Accepted 21 June 2019 urban areas. To control this vehicular exhaust pollution, the end-of-pipe-technology using Available online 6 September 2019 catalytic converters is recommended. The catalysts operating efficiently in a catalytic * Corresponding author. Tel.: þ91 9565243424. E-mail addresses: [email protected], [email protected] (S. Dey). Peer review under responsibility of Periodical Offices of Chang'an University. https://doi.org/10.1016/j.jtte.2019.06.002 2095-7564/© 2019 Periodical Offices of Chang'an University. Publishing services by Elsevier B.V. on behalf of Owner. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 420 J. Traffic Transp. Eng. (Engl. Ed.) 2019; 6 (5): 419e440 Keywords: converter are a challenging class of materials for applications in cold start of engines to Automobile vehicle maintain indoor air quality. In the cold start period, the catalytic converter was entirely Hopcalite catalyst inactive, because the catalytic converter had not been warmed up. The cold start phase is Catalytic converter applications also depending upon the characteristics of vehicles and property of catalysts. The Cold start emission increasing cost of noble metals with the increasing number of vehicles motivates the Carbon monoxide investigation of material concepts to reduce the precious metal content in automotive catalysts or to find a substitute for noble metals. Hopcalite (CuMnOx) catalyst could work very well at the low temperature; thus, it can overcome the problem of cold-start emissions if used in a catalytic converter. Further, low cost, easy availability and advanced synthesis methods with stabilizer, promoter, etc., advocates for the use of hopcalite as an auto exhaust purification catalyst. Although there are numerous research articles present on this topic until now, no review has been presented for demanding this issue. So there is a space in this area, and it has been made an attempt to seal this hole and progress the future scope for hopcalite catalyst for purification of exhaust gases by this review. © 2019 Periodical Offices of Chang'an University. Publishing services by Elsevier B.V. on behalf of Owner. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). reformer gas for fuel cell applications (Aguila et al., 1991). The 1. Introduction performance of catalytic converter is highly depending upon the types of catalysts used. In the presence of catalyst, the Carbon monoxide (CO) is one of the most poisonous and also rate of chemical reaction was increased; it acts like an agent called as the unnoticed poison of the 21st century. With the that reduces the activation energy of the reactions (Faiz increasing number of vehicles on roads, CO concentrations et al., 1996; Kramer et al., 2006). The noble metals (Pt, Pd, Rh, have reached an alarming level in urban areas. An estimate Au, Ag, etc.) and base metals (Cu, Mn, Cr, Co, Ni, Fe, etc.) are has shown that automobile exhaust contributes about 64% of widely used as a catalyst in the catalytic converter. CO pollution in the urbanized countries (Badr and Probert, Commercial catalysts mainly applied for CO oxidation 1995; Benjamin and Alphonse, 2016; Chen et al., 2018). In present in the exhaust gas clean-up are noble metals (Pillai comparison with diesel engine, the petrol engine vehicles and Deevi, 2006). It has a high activity and thermal stability produce more CO into the environment. The CO formed in so that it was widely used as a catalyst in a catalytic internal combustion (IC) engine is operating by the burning of converter. Compared to noble metal catalysts, the hopcalite fossil fuels (petrol or diesel), as an intermediate reaction (CuMnOx) is one of the oldest known catalysts for CO during the incomplete combustion of HC (Cholakov, 2010). The oxidation at low temperature (Royer and Duprez, 2011). The air/fuel (A/F) ratio plays an important role in the efficiency of CuMnOx is broadly used for the respiratory protection combustion process. When an IC engine gets a stoichio-metric systems in many types of applications like military, mining ¼ mixture of A:F 14.7:1, it emits a minimum amount of and space devices, etc. In 1920, Lamb, Bray and Frazer pollutants into the atmosphere (Chhatwal et al., 1975; discovered various mixture oxides of Cu, Mn, Ag, and Co, Ismaila et al., 2013). The natural concentration of CO in air is and identified them as a group of catalysts known as around 0.2 parts per million (ppm), that amount affects not hopcalite (Huang and Tsai, 2003; Zhou et al., 2014). The only the human beings but also vegetation by interface with structure of hopcalite catalyst is also depending upon the plant respiration and nitrogen fixation (Kamrani, 2008). The preparation methods, drying temperature and calcination CO is profoundly affected on the cardiovascular system of conditions of the catalyst. The oxygen species associated human and animal body and combined with hemoglobin with copper in CuMnOx catalyst are very active and may be present in the blood cells and converted into carboxy- dominated by the low-temperature catalytic oxidation of CO hemoglobin (CoHb), which reduces the oxygen-carrying (Dey et al., 2016). capacity of a human body (Pulkrabek, 2004). The chronic The reasons for enhanced catalytic activity are the effect of CO poisoning on human health increases the pulse improved lattice oxygen mobility, specific surface area and rate, respiration system failure, neurological reflexes, pore volume of the CuMnOx catalysts. To improve the reac- headaches and dizziness. After CO exposure, arrhythmias, tivity of lattice oxygen associated with Cu species as well as angina attacks and increase in the level of cardiac enzymes the mobility of lattice oxygen from Mn species (Dey et al., would happen (Air Improvement Resource, Inc., 2005; Alfuso 2017), the Cu-oxide is found weakly active for CO oxidation, et al., 1993; International Council on Clean Transportation but in conjunction with Mn-oxide in appropriate (ICCT), 2016). proportions, very active CuMnOx catalyst system was The ambient temperature catalytic oxidation of CO is a generated (Solsona et al., 2004; Summers et al., 1993). The very important process and is widely applied in automotive air “cold-start” problem controlling the unwanted emissions cleaning technologies, CO detectors, gas masks for fire- produced before the catalytic converter reaches operational fighters, mining application and selective oxidation of CO in J. Traffic Transp. Eng. (Engl. Ed.) 2019; 6 (5): 419e440 421 temperatures. During cold-start phase, about 60%e80% of CO period is called cold-start condition and the high emissions is emitted from automobile vehicle even equipped with a arisen during this period is due to the following reasons. three-way catalyst (TWC) (Dey et al., 2017). TWC which uses noble metals is not being able to function effectively until it 1. Low temperature and high pressure in the engine cylinder reaches the light-off temperature of 200 C as the conversion make it difficult for fuel to vaporize. Hence, the engines efficiency depends strongly on the working temperature and require an enriched mixture to ensure that an adequate is practically zero during the starting and warming up period amount of fuel is vaporized to achieve combustible (Singh and Prasad, 2014). Among the base metal catalysts, mixture. The fuel-rich mixture leads to incomplete com- the hopcalite is highly active for purification of vehicular bustion, resulting in partially burned fuel (CO emissions) exhaust. The addition of ceria (Ce) into CuMnOx catalyst and unburned fuel (HC emissions). increases their performances due to their excellent oxygen 2. Cold-start requires longer engine cranking times that storage capacity (OSC) provided by the redox couple: would be needed at higher temperature. This adds to the 4 þ 2CeO2 Ce2O3 O, making active oxygen available for the emission of incomplete combustion products. acceleration of oxidation reactions and structural 3. Internal friction in the engine and drive train is greater improvement of metal dispersion (Cai et al., 2012). Further, than that at higher temperature, requiring greater power gold (Au) based CuMnOx catalysts show high activity at low output from the engine during warm-up. temperatures, good stability under moisture and resistance 4.