(367g) Environmental Applications of Computational Chemistry

Much research has been done to understand fundamental phenomena in reaction engineering, catalysis, and surface interactions. Unfortunately, the transfer of understanding individual mechanisms on pure surfaces or in controlled homogeneous systems to messy real world applications is often unclear. This is particularly true of environmental applications since interactions may involve solvent effects, multicomponent systems, complex heterogeneous and amorphous surfaces, and electronic interactions that are difficult to probe experimentally. Computational chemistry offers a complementary approach to experimental methods for understanding these complex environmental phenomena.

Current and recent work in this group has investigated a variety of environmentally based problems in order to build a more fundamental understanding on how to remediate systems or on how to prevent environmental degradation due to human activities. Specifically, mercury-chlorine kinetics were examined to predict the importance of mercury speciation in coal combustion flue gases, which is the source of 47 tons of anthropogenic mercury in the United States each year. This homogeneous gas phase work led to more detailed reaction kinetics for a system where experiments are not able to investigate some of the intermediate species. This mercury work led to a further interest in understanding mercury-surface interactions for adsorption technologies to capture mercury at higher temperatures using a sorbent derived from paper waste. This work is investigating how Hg, HgCl, and HgCl₂ interact with the principle components of the novel sorbent: SiO₂, Al₂O₃, and CaO. The work has explored the importance of surface cluster models for predicting adsorption phenomena. A particular challenge has been the treatment of amorphous surface systems reliably while keeping computational costs to a reasonable level. This challenge will intensify as an aggregate surface is constructed from the individual surfaces to simulate the real complexities of this system.

Other ongoing work is investigating the interaction of trichloroethylene (TCE) with iron oxide surfaces as semipermeable iron barriers have been implemented for ground water remediation. The kinetics, mechanisms, and intermediates of degradation of TCE are poorly understood because of the complex phenomena that are difficult to access experimentally. Again, proper construction of a surface model to simulate the iron oxide has been a primary challenge.

Finally, the most recent thrust in research has been in predicting environmental impact parameters, like global warming potentials and ozone depletion potentials from theory. This work combines kinetic estimations from variational transition state theory with spectroscopic predictions in order to obtain numerical values that are indistinguishable from experimental ones at a fraction of the cost. This work has the potential to populate spare databases of environmental impacts so rational green design of chemical processes will be possible.