531
dioxide emissions, which have become significant from the industrial times, total
about 33 Gt/year with contributions from fossil fuel (coal, oil, natural gas) combustion (88%) and net land use change—including deforestation (12%) [3]. Therefore,
CO 2 emissions from natural and anthropogenic sources sum up to about 759 Gt/year.
Natural processes remove CO 2 from the atmosphere at a rate of about 745 Gt/
year include photosynthesis (60%), dissolution of CO 2 in oceans (39%) and rock
weathering (1%) [3]. Presently, no anthropogenic process significantly removes
CO 2 from the atmosphere. Consequently, CO 2 accumulates in the atmosphere at the
rate of 14 Gt CO 2 /year due to the current imbalance between CO 2 emission and
removal rates. This accumulation of CO 2 has been linked to anthropogenic CO 2
emissions (mainly fossil fuel combustion) as before pre-industrial times the carbon
dioxide emission and removal processes were in balance [2, 3, 7].
Amongst the anthropogenic sources, industrial point sources utilizing fossil fuels
contribute 36%, transportation sector 25%, buildings 27% and other sources 12% of
the total CO 2 emissions [8]. Industrial point sources emit significant amounts of
carbon dioxide at individual emission points unlike highly distributed emissions
obtained in transport and building. Table 1 provides a summary listing these industrial point sources and their characteristics. Power plants and various industries produce CO 2 streams with different compositions ranging from a few percent to over
99%. Natural gas processing, ammonia, hydrogen and ethanol production give the
highest concentrations of carbon dioxide while conventional power plants yield the
least concentrations of CO 2 [9].
As shown in Table 1, carbon dioxide is typically emitted in association with other
gases. Even in the air, carbon dioxide is in mixture with oxygen, nitrogen and water
vapour. These other gases are undesirable in the CO 2 utilization processes as they
often act as a diluent. Hence approaches for CO 2 capture to increase its concentration in flow streams need to be explored.
1.4 Carbon Dioxide Capture
Carbon dioxide capture is a terminology used to describe processes that not only
trap but also increase the concentration by separation from other gases in the mixture. Thus, a stream of carbon dioxide with high enough concentration is produced
so that effective utilization or conversion processes can be used. Carbon dioxide
presently can be captured at scale from air and other industrial point sources.
1.4.1 Direct CO 2 Capture from Air
In 2018, carbon dioxide concentration in the atmosphere was determined to be
407.4 ppm. Plants have successfully captured carbon dioxide from air via photosynthesis. Photosynthesis currently account for the capture and conversion of about
450 Gt CO 2 /year. However, CO 2 capture by natural photosynthesis requires
Synthesis of Novel Catalysts for Carbon Dioxide Conversion to Products of Value
dioxide emissions, which have become significant from the industrial times, total
about 33 Gt/year with contributions from fossil fuel (coal, oil, natural gas) combustion (88%) and net land use change—including deforestation (12%) [3]. Therefore,
CO 2 emissions from natural and anthropogenic sources sum up to about 759 Gt/year.
Natural processes remove CO 2 from the atmosphere at a rate of about 745 Gt/
year include photosynthesis (60%), dissolution of CO 2 in oceans (39%) and rock
weathering (1%) [3]. Presently, no anthropogenic process significantly removes
CO 2 from the atmosphere. Consequently, CO 2 accumulates in the atmosphere at the
rate of 14 Gt CO 2 /year due to the current imbalance between CO 2 emission and
removal rates. This accumulation of CO 2 has been linked to anthropogenic CO 2
emissions (mainly fossil fuel combustion) as before pre-industrial times the carbon
dioxide emission and removal processes were in balance [2, 3, 7].
Amongst the anthropogenic sources, industrial point sources utilizing fossil fuels
contribute 36%, transportation sector 25%, buildings 27% and other sources 12% of
the total CO 2 emissions [8]. Industrial point sources emit significant amounts of
carbon dioxide at individual emission points unlike highly distributed emissions
obtained in transport and building. Table 1 provides a summary listing these industrial point sources and their characteristics. Power plants and various industries produce CO 2 streams with different compositions ranging from a few percent to over
99%. Natural gas processing, ammonia, hydrogen and ethanol production give the
highest concentrations of carbon dioxide while conventional power plants yield the
least concentrations of CO 2 [9].
As shown in Table 1, carbon dioxide is typically emitted in association with other
gases. Even in the air, carbon dioxide is in mixture with oxygen, nitrogen and water
vapour. These other gases are undesirable in the CO 2 utilization processes as they
often act as a diluent. Hence approaches for CO 2 capture to increase its concentration in flow streams need to be explored.
1.4 Carbon Dioxide Capture
Carbon dioxide capture is a terminology used to describe processes that not only
trap but also increase the concentration by separation from other gases in the mixture. Thus, a stream of carbon dioxide with high enough concentration is produced
so that effective utilization or conversion processes can be used. Carbon dioxide
presently can be captured at scale from air and other industrial point sources.
1.4.1 Direct CO 2 Capture from Air
In 2018, carbon dioxide concentration in the atmosphere was determined to be
407.4 ppm. Plants have successfully captured carbon dioxide from air via photosynthesis. Photosynthesis currently account for the capture and conversion of about
450 Gt CO 2 /year. However, CO 2 capture by natural photosynthesis requires
Synthesis of Novel Catalysts for Carbon Dioxide Conversion to Products of Value