Question

9.31 The capture of    CO2    by MOFs from post-combustion gas mixtures has been proposed to reduce    CO2    emissions from coal-fired power plants. The challenge is to engineer MOFs that will selectively adsorb    CO2    from these mixtures at relatively low temperatures and pressures, and
subsequently permit facile    CO2    removal to regenerate the MOF for re-use. Describe the synthetic strategy used in T. M. McDonald, W. R. Lee, J. A. Mason, B. M. Wiers, C. S. Hong, J. R. Long, J. Am. Chem. Soc. , 2012 , 134 , 7056 to prepare MOFs with excellent    CO2    adsorption capability. Why do these MOFs require “activation,” and how is this carried out? Why were early attempts with    M2(dobdc)    likely unsuccessful, and how did this inform the design of a new MOF linker?  

Answer 1

MOFs can selectively trap carbon dioxide highly-efficiently and are highly suited to carbon capture from power plant emissions.

The sharply rising level of atmospheric carbon dioxide (CO2) resulting from the burning of fossil fuels is one of the greatest environmental concerns facing our civilisation today. Any serious effort to reduce these CO2 emissions must contend with the geopolitical and economic reality that fossil fuels will continue to make a dominant contribution to the world's energy supply for decades to come. There is therefore a huge global drive to minimise and mitigate these emissions, particularly through Carbon Capture and Sequestration (CCS). CCS involves capturing carbon dioxide that would otherwise be released to the atmosphere, compressing it, transporting it to a suitable site and injecting it into deep geological formations where it will be safely trapped.

The first step in CCS is separating the CO2 from other gases in the exhaust stream and, in the process, capturing the CO2. The dominant technology in these processes has been amine scrubbing; an energy-intensive and inefficient process which creates toxic byproducts. This technology itself requires 30% of the output of the power plant to operate and accounts for as much as 70% of the cost of CCS. These costs must certainly be reduced if CCS is to become viable.

MOFs present a solution to this problem, promising a more environmentally friendly and efficient alternative, capturing more CO2 and requiring less energy to regenerate. The structural tunability of MOFs allows them to be optimised for the specific type of CO2 capture to be performed (post-combustion capture, pre-combustion capture, or oxy-fuel combustion) and potentially even for the specific power plant in which the capture system is to be installed.

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