Conspectus
Climate
change poses unprecedented challenges, demanding efforts
toward innovative solutions. Amid these efforts, chemical looping
stands out as a promising strategy, attracting attention for its CO2 capture prowess and versatile applications. The chemical
looping approach involves fragmenting a single reaction, often a redox
reaction, into multiple subreactions facilitated by a carrier, frequently
a metal oxide. This innovative method enables diverse chemical transformations
while inherently segregating products, enhancing process flexibility,
and fostering autothermal properties. An intriguing facet of this
novel technique lies in its capacity for CO2 utilization
in processes like dry reforming and gasification of carbon-based feeds
such as natural gas and biomass. Central to the success of chemical
looping technology is a profound understanding of the intricacies
of redox chemistry within these processes. Notably, nanoscaled oxygen
carriers have proven effective, characterized by their extensive surface
area and customizable structure. These carriers hold substantial promise,
enabling reactions under milder conditions.
This Account offers
a concise overview of the mechanisms, benefits,
opportunities, and challenges associated with nanoscaled carriers
in chemical looping applications, with a focus on CO2 utilization.
We delve into the nuances of redox chemistry, shedding light on ionic
diffusion and oxygen vacancytwo key elements that are crucial
in designing oxygen carriers. This discussion extends to nanospecific
factors such as the particle size effect and gas diffusivity. Through
the application of density functional theory simulations, insights
are drawn regarding the impact of nanoparticle size on syngas production
in chemical looping. Interestingly, nanosized iron oxide (Fe2O3) carriers exhibit elevated syngas selectivity and constrained
CO2 formation at the nanoscale. Moreover, the reactivity
enhancement of mesoporous SBA-16 supported Fe2O3 over mesoporous SBA-15 supported Fe2O3 is
elucidated through Monte Carlo simulations that emphasize the superiority
of the 3-dimensional interconnected porous network of SBA-16 in enhancing
gas diffusion, thereby amplifying reactivity compared to the 2-dimensional
SBA-15. Furthermore, we explore prevalent nanoscaled carriers, focusing
on their amplified performance in CO2 utilization schemes.
These encompass the integration of nanoparticles with mesoporous supports
to enhance surface area, the adoption of nanoscale core–shell
architectures to enhance diffusion, and the dispersion of nanoscaled
active sites on microsized carriers to accelerate reactant activation.
Notably, our mesoporous-supported Fe2O3 nanocarrier
facilitates methane dissociation and oxidation by reducing energy
barriers, thereby promoting methane conversion. The Account proceeds
to outline key challenges and prospects for nanoscaled carriers in
chemical looping, concluding with a glance into future research directions.
We also shine a spotlight on our research group’s efforts in
innovati...