Calculation of active fractions sizes in supported nanocrystals

Background. The paper is devoted to experimental verification of the possibility of the influence of minor difference between supported nanocatalysts within their carriers’ structure on their functional characteristics, in particular, on the calculated sizes of the active fractions. The oscillatory pattern of CO and hydrogen oxidation, observed in some cases in the presence of platinum metals’ containing nanoparticles, suggests the presence of dissipative structures. It’s known that systems possessed of high complexity (according to Von Neumann), in particular, autocatalytic hypercycles are capable of self-organization. Another sign of such systems’ presence may be a critical influence of minor changes in structure and/or composition on their characteristics. The possibility of such an effect has been verified experimentally: a series of palladium-containing nanocatalysts on activated carbon fibers, differing in particle size distribution, have been synthesized. Carbon fibers obtained from two different precursors were used. Samples from each batch were subjected to reductive treatment with hydrogen at a metered ratio. The boundary sizes of the active fractions are calculated, as well as the activity in the reaction of low-temperature oxidation of CO, at various depths of reduction. Since, for chemically sufficiently inert carbon fibers, a change in the nature of the precursor to the final nanosystems can be considered an insignificant influence factor, a significant effect of such an effect can be considered as confirmation of the hypothesis of the origin of self-organizing systems.
Methods. All calculations were made by using MS Office Professional 2013. A series of palladium nanocatalysts on activated carbon fibers “Busofit Carbopon-Activ” with active surface of 1300 $\text{m}^2/\text{g}$ and Mtilon-M with an active surface of 2700 $\text{m}^2/\text{g}$ was prepared; sizes of nanoparticles varied by choosing modes of drying after application solutions with ions $Pd^{2+}$. The initial reaction rate was measured by gas chromatography from CO concentrations’ decreasing.
Results. The calculation of boundary sizes of nanosystems’ active fractions obtained using the Ball Painting Model showed that carbon fibers’ structure has a significant impact on these dimensions. In nanosystems on Carbopone in comparison with nanosystems on Mtilon-M, not only is the activity shifted towards particles with a smaller diameter, but also a significant narrowing of the size range within which nanoparticles retain activity. Recovery leads to a continuous narrowing of this interval, and therefore the total activity becomes lower with increasing content of the recovered phase. The catalysts applied to Mtilon-M are characterized by a wide size distribution, with unusually large particles showing activity.
Despite the insignificant differences in the structure of the carrier, the characteristics of nanosystems differ significantly. This suggests that more likely are processes with the formation of autocatalytic hypercycles, otherwise one would expect that particles of the same size would be active regardless of the nature of the carrier.
Conclusion. Minor changes in the structure of the carrier matrix lead to significant differences in the characteristics of nanocatalysts - the boundaries of the active fractions are mutually shifted, and the interval of the boundary sizes can be both wide enough and extremely narrow. This is consistent with the hypothesis of the formation of autocatalytic hypercycles, the level of complexity of which suggests that they are self-organizing.
Implementation opportunities. High toxicity, lack of color and smell, low adsorption and chemical passivity of CO make it one of the most dangerous toxins. The removal of CO in practice is seriously difficult, and the use of nanocatalysts for life-support and respiration systems is practically non-alternative in this aspect. A reliable method of obtaining self-organizing high-performance nanosystems capable of removing CO under room conditions would be used to clean the atmosphere of closed living spaces - in cars, spaceships, submarines, in industrial workshops, and others. Considering that for almost all other gaseous toxins, with the exception of CO, robust removal systems have been developed, filling this gap will allow creating universal filters for life support systems.
Social consequences. Work in this direction can be a solution to a number of social problems, including health safety while in traffic jams, especially for risk groups.
Originality/value. Proof of hypercycles’ formation at a high level of complexity capable of further self-organization, and their careful study is of great theoretical importance for understanding the possibilities that open up for non-equilibrium dissipative systems - it is possible that they can be compared with questions about the origin of life and the evolution of hypercycles in nature. The study of the influence of the nature of carbon fiber precursor on the behavior of hypercycles seems rather unexpected, but nevertheless remains fruitful.