It is crucial to control NO_x emission into the atmosphere because it can make several harmful health and environmental effects. Many techniques are available for NO_x reduction, and among them, selective catalytic reduction (SCR) is one of the most efficient techniques for NO_x removal in flue gas cleaning process. The reduction of NO_x by CO offers a simple and low-cost technology for reducing NO_x emissions from mobile or stationary sources. In this review, NO_x emission, different NO_x control technologies, and the challenges for the SCR process are studied. This paper reviews various types of catalysts, including supported and unsupported metal oxide catalysts as efficient catalysts for NO_x reduction by CO. The reported experimental researches are analyzed to make an overview of the NO_x reduction through CO-SCR process. Moreover, catalytic performances in the presence of oxygen, water steam, and sulfur dioxide, which usually exist in exhaust gases produced in the combustion process, are discussed. Moreover, this paper reviews the possible reaction mechanisms for the CO–SCR.

Light olefins are the main building blocks used in the petrochemical and chemical industries for the production of different components such as polymers, synthetic fibers, rubbers, and plastic materials. Currently, steam cracking of hydrocarbons is the main technology for the production of light olefins. In steam cracking, the pyrolysis of feedstocks occurs in the cracking furnace, where hydrocarbon feed and steam are first mixed and preheated in the convection section and then enter the furnace radiation section to crack to the desired products. This paper summarizes olefin production via the steam cracking process; and the reaction mechanism and cracking furnace are also discussed. The effect of different operating parameters, including temperature, residence time, feedstock composition, and the steam-to-hydrocarbon ratio, are also reviewed.