Biocatalysis of CO2 and CH4: Key enzymes and challenges

Mitigating greenhouse gas emissions is a critical challenge for promoting global sustainability. The utilization of CO2 and CH4 as substrates for the production of valuable products offers a promising avenue for establishing an eco-friendly economy. Biocatalysis, a sustainable process utilizing enzymes to facilitate biochemical reactions, plays a significant role in upcycling greenhouse gases. This review provides a comprehensive overview of the enzymes and associated reactions involved in the biocatalytic conversion of CO2 and CH4. Furthermore, the challenges facing the field are discussed, paving the way for future research directions focused on developing robust enzymes and systems for the efficient fixation of CO2 and CH4.

Bio-Inspired Microreactors Continuously Synthesize Glucose Precursor from CO2 with an Energy Conversion Efficiency 3.3 Times of Rice

Excessive CO2 and food shortage are two grand challenges of human society. Directly converting CO2 into food materials can simultaneously alleviate both, like what green crops do in nature. Nevertheless, natural photosynthesis has a limited energy efficiency due to low activity and specificity of key enzyme D-ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). To enhance the efficiency, many prior studies focused on engineering the enzymes, but this study chooses to learn from the nature to design more efficient reactors. This work is original in mimicking the stacked structure of thylakoids in chloroplasts to immobilize RuBisCO in a microreactor using the layer-by-layer strategy, obtaining the continuous conversion of CO2 into glucose precursor at 1.9 nmol min-1 with enhanced activity (1.5 times), stability (≈8 times), and reusability (96% after 10 reuses) relative to the free RuBisCO. The microreactors are further scaled out from one to six in parallel and achieve the production at 15.8 nmol min-1 with an energy conversion efficiency of 3.3 times of rice, showing better performance of this artificial synthesis than NPS in terms of energy conversion efficiency. The exploration of the potential of mass production would benefit both food supply and carbon neutralization.

A versatile optofluidic microreactor for artificial photosynthesis induced coenzyme regeneration and L-glutamate synthesis

With the rapid development of modern society, the energy crisis has become a global concern. Solar energy is a good replacement because it is green, unlimited and environment-friendly. Inspired by natural photosynthesis, artificial photosynthesis was developed to convert solar energy to chemical energy by a photocatalyst system. For better utilizing solar energy and improving the conversion efficiency, the design of photoreactors is crucial for the improvement of photocatalysis efficiency. However, most of the reported microreactors hardly satisfy the demands for low cost, easy fabrication, high transparency, being evaporation-proof, ease of scaling up, high surface-to-volume ratio, and photocatalyst immobilization. In this paper, we developed a facile method to build a fully immobilized microreactor (FIM) and a controllable partially immobilized microreactor (PIM), both of which satisfy all the demands mentioned above. In the FIM, the regeneration rate of a coenzyme (nicotinamide adenine dinucleotide, NADH) reached 82.20% in 40 min. Considering the NADH regeneration rate per unit/coating angle of photocatalysts in circular microreactors, the PIM performed much better than the FIM, proving that our partial coating method is a significant and useful improvement. Also, the bioactivity of NADH toward enzyme catalysis was demonstrated by glutamate dehydrogenase-catalyzed synthesis of L-glutamate, and the conversion of α-ketoglutarate reached 99.92%. To test the practicality of the microreactor in a real environment, we performed a test under solar light, achieving a good result of 74.92% in 60 min. Thus, this efficient and versatile microfluidic platform may have good potential for photocatalytic synthesis of versatile valuable products in the future.