Carbon dioxide (CO2) emissions and climate change

Carbon dioxide (CO2) emissions and climate change

Abstract

Among the most significant challenges the world faces throughout its history is climate change. Also, it a fundamental problem for the sustainable development process, which is concerned with achieving economic and social aspects. Development is one of the high aims that many countries of the entire world want to make, but they omission the environmental dimension to conserve natural resources for the benefit of future generations. The thematic of the present study is to review the different methods that investigate the reduction of Carbon Dioxide (CO2) by using transition metal complexes. Most of these complexes, molecular catalysts, are light-sensitive and suffer from photostability issues by ligand photodissociation reactions and photoisomerization. This particular problem is an essential obstacle towards the efficient metal complex photocatalysts for CO2 reduction advancement. Unarguably, more improvements are still required, and other pathways for CO2 catalytic reduction may perhaps offer ample fruitful opportunities. One of the possible means to achieve this stability could be to ensure heterogeneous complexes. Although using metal complexes catalyzes and activate small molecules is a relatively small field, this strategy demonstrates a high promise of achieving a reaction that may be challenging by other means. Transition metals are among the most investigative elements, as manganese, chromium, and copper appear to be less frequent.

Contents

Abstract ………………………………………………………………………………………..2

1-Introduction …………………………………………………………………………………4

2-Carbon dioxide properties ………………………………………………………………….6

3- A brief look at the hazards of global increasing carbon dioxide……………………..7

3.1 Carbon dioxide and climate change…………………………………………..7

4- Transition metal complexes………………………………………………………………9

5- Selective photocatalytic systems and electrocatalytic co2 reduction: state of the art..9

5.1 Fourth and Fifth Row in transition metals………………………………………11

5.1.1 complexes of Ru………………………………………………………. 11

5.1.2 Complexes of Os, Rh, and Ir…………………………………………12

5.1.3 Complexes of Re………………………………………………………….13

6-Complexes from the first row in tarnation metal ……………………………………….14

7-Conclusion……………………………………………………………

8- References………………………………………………………………………………….

1-Introduction

Carbon dioxide (CO2) emissions continue to rise and contribute to adverse impacts on the environment, one of which is the shift to harsher climatic conditions than global warming. It is due to human resources in the ever-increasing use of fossil fuels, which has been our main source of non-renewable energy. Therefore, there is a need to research renewable and clean sources of energy to reduce the emission of carbon dioxide into the atmosphere. However, the challenge for researchers is the high activation energy barrier to activate carbon dioxide for subsequent conversion into chemical precursors and fuel precursors. Researchers aim to develop abundant Earth transition metal catalysts that will effectively reduce carbon dioxide electrically into more useful, high-activity products (Zhang, 2015). The excessive reliance on non-renewable fossil fuels and climate change requires long-term solutions to reduce carbon dioxide emissions and develop alternative and renewable fuels. There is, therefore, a need to reduce greenhouse gas emissions and the urgency to reduce the community’s dependence on rapidly diminishing fossil fuels. Renewable energy is currently one of the most important research topics in the world because the excessive use of fossil fuels containing carbon and its products in both transport and industry sector has led to the uncontrolled release of carbon dioxide (CO2) into the atmosphere, contributing meaningfully to global warming and climate change. One of the most serious concerns which could potentially drive the Earth into a new system is greenhouse gas emissions. Excessive use of carbon-containing fossil fuels and products in the transport and industrial sector has led to uncontrolled emissions of carbon dioxide (CO2) into the atmosphere, contributing significantly to climate change and global warming. The most important anthropogenic global warming gases are carbon dioxide, with an estimated thirty-five gigatonnes of human sources released in 2012. More than three times that amount, an estimated one hundred and twenty-two gigatonnes of carbon dioxide, is reflected in the Earth’s built environment. Scientists have observed a significant increase in carbon dioxide emissions since the beginning of manufacturing. Carbon dioxide (CO2) is a major participant in the greenhouse effect process. Besides the natural process of carbon dioxide origin, for example, human and plant respiration, animal respiration, soil degradation, evaporation from the ocean, various human activities have had a significant impact on carbon dioxide emissions. The process and increased use of transport, the burning of fossil fuels, and plant manufacturing processes have an irreversible impact on our planet, resulting in a dangerous level of atmospheric emissions. Numerous studies to reduce CO2 are reviewed by homogeneous early transition complexes (groups 3-7). Several interactions with CO2 have been studied using delayed transition metals (groups 8-10), and significant progress has been made in the development of active and selective homogeneous catalysts for CO2 reduction with delayed metals. However, the main drawbacks of these systems are that they only produce carbon dioxide or format products. By comparison, early transition metal complexes were neglected to develop carbon dioxide reduction catalysts; there are few studies that have been researched in the field of transition metal complexes. For the above reasons and the adverse impact of CO2 emissions on the environment, there is a great need for a way to reduce the amount of CO2 in the environment and its emissions; therefore, the problem lies in the reduction of Carbon Dioxide (CO2) by transition metal complexes. This literature review will start describing the chemical and physical properties of carbon dioxide briefly. Next will focus on the effect of the increase of carbon dioxide in the air. Finally, an in-depth review of some studies on reducing carbon dioxide by using metal complexes that will be presented to understand the art of catalyst development in this area.

2- Carbon Dioxide Properties / Carbon dioxide is a chemical compound of oxygen and carbon with the chemical formula CO2. Under standard pressure and temperature conditions, carbon dioxide is colorless, odorless, non-flammable, acidic, and easily dissolved water. CO2 is an average of 0.040% of the atmosphere, equivalent to 400 ppm, as shown in table 1. As part of the carbon cycle, plants and algae use the energy of light to photosynthesize the sugars from carbon dioxide and water, resulting in the formation of oxygen as the product of the process. In contrast, photosynthesis does not take place in the dark, and plants produce carbon dioxide at night during cellular respiration. Also, carbon dioxide is produced through the exhalation of humans and other aerobic organisms. Carbon dioxide is also produced during the decomposition of organic materials during the fermentation of sugars as a product of the combustion of wood, sugars, and most of the carbon-rich fossil fuels, such as coal, peat, oil and natural gas. CO2 is also emitted from volcanoes, lava, and sour eyes (heaters). It is released from carbonate rocks when dissolved in acids, as well as in lakes, and the deep sea combined with oil and gas deposits (Leung, 2019). There are many applications of carbon dioxide in the food, petroleum, and chemical industries. For example, CO2 uses in the production of urea, the food industry for the manufacture of soft drinks and spirits. Besides, supercritical carbon dioxide is used as a solvent and as a means of extraction in chemistry, and dry ice, solid-state carbon dioxide, is used as a refrigerant. Carbon dioxide is a very stable compound that needs a huge amount of energy to convert into another chemical compound. It is also a linear molecule (O = C = O) since the carbon atom is bound to two oxygen atoms by a covalent bond and is the C-O bond. It is Stronger than the bond between an O – O and a C – C with C = O [= 187 (2 × 93.5) kcal / mole] O = O [= 116 (2 × 58)] and C = C [= 145 (2 × 72.5)] respectively.

3- A brief look at the hazards of global increasing carbon dioxide.

In recent years humans have relied on oil extraction and construction of factories, which has led to the reconstruction of the Earth and led to the growing demand for energy production. Where many disciplines are involved in trying to understand the implications of human activities. Consequently, these studies led to numerous observations of change in the Earth’s system. The most important of these changes, which change over time and since the industrial revolution, is the release of carbon dioxide in the air atmosphere. Increased carbon dioxide (CO2) is a complex problem that scientists are seeking to solve, causing many problems in the Earth’s system.

3.1 Carbon dioxide and climate change

Carbon dioxide emissions have increased beyond their ecological capacity since the advent of the industrial revolution. Like carbon dioxide, a greenhouse gas is one of the critical aspects of climate change that has caused global warming. It is also a fundamental challenge for the sustainable development process, which is concerned with achieving economic and social aspects without neglecting the environmental dimension to preserve natural resources for future generations. It is a development that is keen on social justice and which the people of the whole world dream of achieving their goals. Studies show that the burning of all forms of fossil fuels (coal, petroleum, natural gas) is known to be the primary source of CO2 emissions, and some agricultural and livestock activities constitute a significant source of atmospheric methane emissions. Discriminate these gases to the high degree of global warming by 0.6 degrees Celsius since the beginning of the measurement of these gases operations. Many climate scientists, meteorologists, and others have studied climate change and filled them more than half a century.  The phenomenon of climate change is distinguished from most other environmental problems as it is global, as it has exceeded the borders of countries to pose a danger to the whole world. For example, in 2016, the researcher pointed out the effect of increasing the temperature in the atmosphere. This study indicated the use of a diagnosis of 1%. They showed the difference in the concentration of carbon dioxide and the difference in temperature as the concentration of carbon dioxide 0.35 ppm. Also, some climate research has been devoted to gaining knowledge from further studies on climate impact by increasing the level of carbon dioxide. Having conducted a survey to calculate heating degree days and cooling degree days in 29 provinces in China from 1995 to 2011, using the degree-day method. The findings of the estimated indicate that the impact of climate change feedback on China’s carbon emissions is statistically significant but not massive. During the sample period between 1995 and 2011, it can be approximately 1.687% of China’s total carbon dioxide emissions attributed to climate change. Moreover, the effects of climate change on different regions of China are markedly different. Some strategies help reduce carbon dioxide emissions using chemical compounds, while some seek solutions to convert them into useful compounds by using catalysts. One of the most critical research conducted in an attempt to reduce carbon dioxide. It is done by using metal complexes in photocatalytic systems and electrocatalytic.

4- Transition metal complexes

The largest group of elements present in the periodic table are transition metals. They got their name because the English chemist Charles Bury described a chain of transition in 1921. Bory studied the transition from the inner electron layer with 8 electrons to a layer of 18 electrons and formed a layer of 18 electrons to one with 32. The transitional element is defined as transitional atoms whose composition ends in an electron, and their benefits vary according to the type of transitional element.

Metallic complexes shown in red include catalysts for photochemical reduction. Figure 2B shows examples of metallic complexes as catalysts for CO 2 reduction. These metal-based catalysts are sometimes called “molecular catalysts” because they can be designed at molecular levels by choosing metal elements and bonds (Ishida, 2018.

The conversion of carbon dioxide into beneficial chemicals is highly needed as a result of increasing global temperature and rising levels of carbon dioxide in the atmosphere. However, CO2 is dynamically inert and dynamically inactive, and therefore, much effort has been made in the last few decades (Leung, 2019). Carbon dioxide repair/hydrogenation is widely used as a means to access valuable products such as acetic acids, CH4, CH3OH, and CO. Electrochemical reduction of carbon dioxide using heterogeneous and heterogeneous catalysts has recently attracted much attention. In particular, molecular catalysts for CO2 reduction have been studied extensively using modified metal transition complexes with different bonds to understand the relationship between different catalytic properties and the coordination areas above the mineral centers. At the same time, the association of carbon dioxide with varying types of electricity under homogeneous conditions is also a meaningful way to recycle carbon dioxide as a renewable C-1 substrate in the chemical industry. Carbon dioxide reduction methods can be broadly classified into four main categories: reduction of thermal, biochemical, photochemical, and electrochemical chemistry. There are thermal, chemical methods to reduce carbon dioxide for several decades. One known example is the conversion of carbon dioxide and H2 into methanol under a catalyst generally composed of Cu / ZnO / AlO3, which can be said to be similar to the current industrial method of producing methanol from syngas. This conversion process requires temperatures and pressures around 220−330 °C and 50−100 atm, respectively. As expected, due to unusual operating conditions, high-density thermal, chemical methods in energy consumption. Therefore, at present, times are still fossil-fuel more convenient and efficient. With these considerations, this review will focus on some survey the literature for molecular homogeneous CO2 reduction catalysts. For price and simplicity consideration, and given the vastness of this area of chemistry, it will restrict that to homogeneous metals complexes that have been reported to facilitate catalytic CO2 reduction.

5- Selective photocatalytic systems and electrocatalytic CO2 reduction: state of the art

The natural processes carried out by the Earth eliminate carbon dioxide through plants, ocean water, soil, and also rocks. Some strategies help reduce carbon dioxide emissions using chemical compounds, while some seek solutions to convert them into useful compounds by using catalysts. One of the most critical research conducted in an attempt to reduce carbon dioxide was used metal complexes in photocatalytic systems and electrocatalytic. In this part will present some studies on the varies catalysts which have been reported on metals. Therefore, it will divide by each metal such as Ru and Re catalysts that have been extremely studying well and then will focus on present some publication to determine structures and active species.

5.1 Fourth and Fifth Row in transition metals

5.1.1 Ru complexes

Many years ago, researchers conducted many studies of Ru complexes; thus, [Ru (bpy) 2 (C.O.)n(X)m] (2 –m) + had much attention to use it as catalysts of reducing carbon dioxide. Ishida et al. carried out two complexes, which are [Ru(bpy)2(C.O.)Cl] +and [Ru(bpy)2(CO)2]2+ (as shown in figure 2), and they used them in a solvent mixture of H2O/DMF with (90:10, v: v). The electrolyzes performed at −1.50 V vs. SCE under the pH of the solution. The pH was six as acidic conditions; thus, they observed a mixture of C.O. and H2 while using a pH of 9.5 as basic conditions gave formate.

[Ru(bpy)2(C.O.)(COOH)] + was proposed as selectivity determining intermediate, describing as [Ru(bpy)2(C.O.) (CO2)]0 in the protonation of the carbon dioxide (figure 3). [Ru(bpy)2(C.O.)(COOH)] + was proposed as selectivity determining intermediate, describing as [Ru(bpy)2(C.O.)(CO2)]0 in the protonation of the carbon dioxide. Using acidic state causes more protonated to the yield, which presented H2O and [Ru(bpy)2(CO)2]2+ equivalently. In contrast, under the essential condition, the reacting of [Ru(bpy)2(C.O.)(COOH)] +, proton, and two-electron to produce HCOO- and [Ru(bpy)2(C.O.)]0. In these mechanisms reported more than 84.3% of formate if using Me2NH∙HCl. However, CO and H2 produced with strong acids.

Additionally, in react years, there are two complexes of Ru used as catalysts to reduce CO2. these two complexes are [Ru(tpy)(by)(Solvent)]2+and [Ru(tpy)(3-methyl-1-pyridylbenzimidazol-2-ylidene) (Solvent)]2+. These two catalysts performed a high activity at −1.52 V vs. in MeCN after 5 hours CO displayed 76%. In the existence of H2PO4−, these complexes can reduce protons that caused the synthesis of H2 and C.O. by using electrolyze a CO2 in MeCN with H2PO4− in solution. According to researches, because many of Ru complexes act in the same way, there are studies suggested different products to reduce CO2. In 2006, Gibson and collaborators suggested this compound [Ru(tpy C.O.)(bdy)(CO0]+ as intermediate to convert CO2 to C.O. by isolated a Ru(tpy)(bpy) C.O. that has covalently bond between Ru and N. Using Ru complexes as catalyses to decrease CO2 is distinguished and valuable compounds. The studies continue to investigate different sides of these complexes.

5.1.2 Complexes of Osmium, Rhodium and Iridium

Since Ru systems were successful, Os complexes studied to support reducing CO2.  For example, Deronzier and Chauvin investigated photocatalytic to decrease CO2 by using osmium. They performed it by using trans (Cl)-[Os(dmbpy)(CO)2(Cl2)] and trans (Cl)-[Os(bpy)(CO)2(Cl2)]. These complexes did in DMF, TBAPF6, and TEOA as supporting electrolyte and electron donor respectively to produce C.O.

Moreover, Rhodium and Iridium, which are metal in the second and third row of transition, have been studied as successful complexes to achieve a reduction of CO2 considering as electrochemical. Deronzier et al. used Rh and Ir complexes in mixtures of MeCN/H2O to reduce CO2. As a result, H2 and formate with less C.O. were shown.

Overall, the investigation of these complexes is still in development. However, Os, Rh, and Ir are the most complexes in the 4d and 5d transition metal achieved to reduce CO2.

5.1.3 Complexes of Rhenium

According to the review, the Re (by)(C.O.)3X is one of the most common Re catalysts used to reduce CO2. This class can be electrocatalyst and photocatalyst. For example, Lehn, Ziessel, and Hawecker indicated using a mixture including Re(bpy)(C.O.)3Cl, DMF/water, and Et4NCl to reduce CO2 to CO over 90% faradic.

However, they mentioned that if the solution has much water, it will affect the result of CO. Furthermore, through time, researchers continue to study Re complexes for reduction CO2. Recently, in 2019, Yasmeen et al. reported that cis-[Re(bpy)2(CO)2]+OTf (1+OTf) was able to reduce CO2 (figure). They observed that using this complex under visible light led to form formic acid, which produces C.O. Overall, Re-complexes are generally a great catalyst to decrease carbon dioxide. However, the mechanism still considers it because it is governed by the selectivity of C.O.

6-Complexes from the first row in tarnation metal

Scientists face a fundamental challenge to reduce CO2 by using chemical compounds because of environmental concerns. Therefore, they focus on photocatalysis and electrocatalysis, such as Mn, Fe, and Ni, to create complex to solve that problem. First, the first row of metal has been interested in this field, so Mn complexes are electrocatalyst, which has involved in CO2 reduction. Kubiak and his group studied the catalytic activity in promoting proton in solution under the weak of Brönsted acids condition, so they were able to use this mechanism to reduce CO2. In addition, 4-phenyl-6-(1,3-dihydroxy benzene-2yl)-2,2′-bipyridine (dhbpy) and 4-phenyl-6-(1,3-dimethoxy benzene-2yl)-2,2-bipyridine (dmobpy) were reported as origin local proton and control without proton respectively (shown in figure); thus, the first one showed the ability to CO2 reduction while the second complex was not active. Local proton source existence appeared the efficiency with 70% and 22% faradic for C.O. and formate.

In recent year, Gyandshwar et al. pointed out two complexes of Mn which, are MnBr{k2-(Ph2P)NMe(NC5H4)}(CO)3 and Mn{k3-[2,6-{Ph2PNMe}2(NC5H3)]}(C.O.)3+Br- (1+Br-),(figure) were successful in achieving reduction of CO2 with 96% for the second compound. In contracts, MnBr{k2-(Ph2P) NMe(NC5H4)}(CO)3 was produced C.O. and H2 with present water. Many types of research showed the efficiency of Mn complexes to CO2 reduction, although Mn-by is still in the study.

Furthermore, Reports maintained that Co, Fe, and Ni systems have analogous assessments to CO2 reduction. In 1992, Ni complexes showed an increase of cathodic current with CO2 in this study, so it has been used –1.54, –1.20, and –1.80 V vs. SCE of the potentials to reduce CO2. One of the recurring problems reported by many workers about electrochemical CO2 reduction is the deactivation of the CO2 reduction reaction, where the overall CO2 reduction and selectivity decrease over time in favor of HER. Losing of CO2 reduction activity was not unique to copper electrodes and has also been observed in other widely studied metal electrodes such as Au and Ag (Kas, 2015). The date range in which deactivation occurs varies widely between reports, from at least 10 minutes to gradual deactivation over several hours (Lim e. a., 2016). Although copper is unique in comparison to other minerals in terms of its ability to reduce carbon dioxide, in the sense that it can reduce carbon dioxide to more than just C.O. and HCOO−, it does not do so efficiently (with high trailing potential) Selective impairment. Therefore, considerable efforts have been made in the characterization and design of copper-based P.V. catalysts that retain the unique catalytic potential of copper while improving the efficiency and transition of the CO2 reduction reaction.

One approach is to design bimetal catalysts or copper alloys. In general, copper alloys using another metal have shown that they significantly reduce the excess potential of the formation of carbon dioxide reduction products (Hirunsit, 2015). Although most copper alloys do not show significant improvements in product selectivity toward hydrocarbons (CH4 and C2H4), some alloys are capable of generating products that cannot be manufactured by individual metals separately in detectable quantities (Jia, 2014). Another approach to improving copper performance involves the application of copper oxides. The oxidized copper surfaces examined were prepared in different ways, the most common being through thermal air oxidation, aluminum oxide, and electrical corrosion. Among these methods, Lu et al. were discovered that methanol yields and current efficiency (38%) are highest in electrolytic copper oxide (I) films. They suggested that the active sites in Cu (I) may play an essential role in selectivity toward methanol by stabilizing key intermediates such as methoxy and by acting as hydrogen-donor sites that promote the reduction of methoxy to methanol (Lim C. F., 2017) — experimentally observed selectivity towards methanol on copper oxide surfaces. DFT theoretical simulations have recently explained it since the preference towards methanol over methanol over CH4 (from the methoxy medium) on oxidized copper surfaces is due to the weak oxygen-binding strength of the methoxy to the electrode Surface (Zhang, 2015). Despite the apparent selectivity towards methanol, the apparent problem in the use of copper oxide surfaces is their poor stability in cathodic conditions to reduce carbon dioxide, during which copper oxides are entirely reduced to copper metal. Although there are many arguments claiming that a small amount of copper oxide can persist (Lee, 2015) or even form while reducing carbon dioxide (possibly because carbon dioxide is It is a semiconductor),methanol production is generally not observed after the majority of copper oxide has been reduced to metallic copper (Lim, 2017).

Conclusion

The review offers an overview of the past research on the complex molecular catalysts of metals to reduce carbon dioxide contributions to the growing and dynamic field that is gaining new insights into science at an ever-increasing rate. To increase the use of molecular catalysts of metal complexes, their bad stability, which is a significant challenge, must be overcome. Suggesting that one of the possible means to achieve this stability can be to ensure heterogeneous complexes, although the use of low-coordinate metal complexes to catalyze and activate small molecules is a relatively small field; this strategy demonstrates a high promise of achieving a reaction that may be challenging by other means. Indeed, a wide range of exciting and diverse transformations have been discovered, and feel confident that this area of research will continue to grow and develop in the future. One thing that noticed during the formation of this perspective is the relatively narrow range of three-dimensional metals that dominate this region. Rhenium and manganese are among the most investigative elements, as chromium and copper appear to be less frequent, which explored elements that can result in an invisible interaction and hope to see more work in this area in the future. It is very likely that the development of new large bonds with different electronic properties. Also, the key that will help to improve the development of low-coordinated catalysts and detectors in the future. Finally, the growing interest in mechanical investigations of these catalysts will enable researchers are making kinetic measurements of these systems rather than merely presenting the reaction. Hoping will lead to a greater understanding of the factors that support the interaction of low-coordinate mineral species and allow the rational design of improved catalytic systems in the future.

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