Branched catalytic reaction networks with oscillating chemical pathways perfectly select for reaction products at varying frequency.

Instructions for contributors Inside back coverCover illustration. Hierarchical zeolites made of intergrown nanosheets offer short diffusion lengths allowing for catalytic reactions to proceed in the zeolite micropores in the absence of diffusion limitations. At the same time, catalysis of desirable or undesirable reactions can take place in the mesopores. Using a model reaction and by systematic variation of nanosheet thickness with nanometer (single-unit-cell) precision, it is demonstrated that reaction-diffusion in micro-/meso-porous zeolites can be quantitatively analyzed by mathematical modelling, and finetuned towards a desirable product distribution. Images courtesy of Dandan

The catalytic conversion of biomass-derived furfural to 1,3butadiene is a potential synthetic route to renewable rubber. In this work, we present and evaluate a conceptual process design consisting of three steps: (i) decarbonylation of furfural to furan, (ii) hydrogenation of furan to tetrahydrofuran, and (iii) dehydra-decyclization of tetrahydrofuran to 1,3-butadiene. Detailed reaction and separation systems are designed using process simulation and economic optimization. At a scale of 77 kton year −1 of furfural (100 kmol h −1 ) purchased at $1.84 kg −1 ($176 kmol −1 ), a minimum sale price of butadiene of $5.43 kg −1 is calculated. The selectivities of the decarbonylation and dehydradecyclization catalysts are identified as the key process parameters by performing a sensitivity analysis on the minimum selling price of butadiene. Economic and technological factors necessary to achieve a minimum sale price of butadiene below $1.50 kg −1 ($81 kmol −1 ) are identified. A quantitative treatment of process sustainability results in a carbon efficiency of ∼58% and an E-factor of ∼1.5 for the overall process.

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Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10^-6 < f < 10⁴ Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

Experimental modeling and subsequent analysis of microevolutionary processes often involves estimation of fitness components, such as male mating competitiveness, female fecundity, progeny viability, meiotic drive upon the formation of sexual products, and so on. In this connection, we have developed a new method for estimating the relationship among fitness components and their effect on selection on frequencies of the mutant individuals in several generations, which can be applied to the case of rapid elimination of a lethal mutation from the population. The method of estimating unknown fitness components is based on the known estimates of other components and a relationship among the known and unknown components calculated from the frequency dynamics. Using the new method, a biological explanation of non-uniqueness of the admissible solutions. The method employs analysis of the form of the admissible solution region (at preset confidence intervals for the observed frequencies) in the space of the possible values.

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