1 Carbon Dioxide Reduction and Uses as a Chemical Feedstock

The utilization of carbon dioxide (CO2) as a source of carbon in synthetic chemistry has been a practice exploited at the industrial level since the second half of the 19th century for the synthesis of urea [1a] and salicylic acid [1b, c]. CO2 has also long been used for making inorganic carbonates and pigments. A renewed interest in the industrial utilization of CO2 as a source of carbon arose after the 1973 oil crisis. The topic has been comprehensively reviewed by several authors [2]. A critical assessment of CO2 utilization is also available [3]. CO2 is ubiquitous – it can be either extracted pure from natural wells or recovered from various industrial sources. For instance, quite pure CO2 is recovered from urea synthesis. Several other industries, such as those using fermentation or similar methods, also provide a convenient source of pure CO2 (above 99%) at low recovery cost, but their seasonality prevents full exploitation so that several million tons per year (Mt year) of pure CO2 are vented. Today, there is a growing interest in recovering CO2 from power station flue gases that contain around 14% of CO2, but the separation techniques are quite expensive [4] and are seldom applied on a large scale [5]. In recent years, CO2 has also found growing application as a technological fluid in several industrial sectors, such as a cleaning fluid, in refrigeration, air conditioning and fire extinguishing equipment, as a solvent for reactions, as a solvent for nano-particle production, and in separation techniques and water treatment, as well as in the food and agro-chemical industries (packaging, additive to beverages, fumigant) [6, 7]. In all such technological applications, CO2 is not converted and can be recovered at the end of the application or vented to the atmosphere. Most of the CO2 used for such applications is currently extracted from natural wells, yet it is highly desirable to substitute the extracted CO2 with that which is recovered from power stations or industrial processes. This would be in line with the need to reduce its emission into the atmosphere – a worrying accumulation since the beginning of the industrial era [8]. How 1