Evaluation of stability of silica-supported Fe–Pd and Fe–Pt nanoparticles in aerobic conditions using thermal analysis

The applications of zerovalent iron nanoparticles (nZVI) exploit their high reactivity which decreases due to oxidation in aerobic conditions during manufacture, application, and storage. In this study, we present the new procedure for estimation of the nZVI stability to oxidation in air. The procedure is suitable for characterization of the novel materials based on the supported nZVI. Nanoscale particles were synthesized inside porous silica supports by incipient wetness impregnation with the metal precursor solutions followed by thermal treatment. The TG–DTA studies revealed the decomposition temperature of the supported precursors, as well as the interaction of Fe and precious metal precursors, which resulted in the formation of alloy nanoparticles. Characterization of the samples by XRD confirmed the formation of the nanoparticles of the metallic Pd, Pt, and Fe phases supported on SiO₂ carriers, as well as the formation of solid solutions based on the structure of precious metals. The new procedure for estimation of the nZVI stability included (1) TPR with hydrogen up to 400–425 °C followed by isothermal reduction at these temperatures; (2) in situ reoxidation with oxygen at room temperature. The samples were reduced “as obtained” and after in situ reoxidation. The results of the TPR studies exhibited that introduction of both Pd and Pt protected the Fe nanoparticles from oxidation with oxygen and air at ambient conditions.     

Properties of pentasil-containing catalysts in hydrocarbon conversions 6. Formation of condensation products during aromatization of propane on pentasils modified by zinc and gallium

Condensation products (CP) formation during the aromatization of propane on pentasils modified by Zn and Ga (1–5%) has been studied by IR spectroscopy, and thermal and chemical analyses. The amount of CP increases with increasing Zn concentration but falls with increasing Ga concentration in the catalyst. CP are formed both in the channels and on the exterior surfaces and are of an aromatic nature. Coking occurs to a greater extent and the CP are more dehydrogenated for Zn-containing samples than for those containing Ga. A relationship has been noted between the processes of formation of condensed aromatic hydrocarbons, CP, and methane.For previous communication, see [1].Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1962–1967, September, 1991.     

Estimation of the dead time period and parameters of an asynchronous alternative flow of events with unextendable dead time period

A problem of estimating the parameters of an asynchronous alternative flow of events with initiation of a superfluous event being a mathematical model of information flows of queries circulating in integrated service digital networks as well as a mathematical model of fluxes of elementary particles (photons, electrons, etc.) arriving at the recording equipment is considered. The conditions of flow observation are such that each registered event generates a dead time period during which other flow events are unobservable. The case of unextendable dead time period is investigated. The probability density of interarrival time in the flow under observation is found. The parameters of the initial asynchronous alternative flow with initiation of a superfluous event and a dead time period are estimated by the method of moments. Results of a statistical experiment realized for an imitational model are presented. They demonstrate fairly good properties of the estimates obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 35–49, October, 2005.     

Synthesis and the Crystal Structure of a New Chiral 1D Metal–Organic Coordination Polymer Based on L-Prolineamide-Substituted Diarylacetylenedicarboxylic Acid Derivative

The new homochiral 1D metal–organic coordination polymer [Cu₂(EDPB)•H₂O]_n was synthesized starting from the original 3,3′-ethyne-1,2-diylbis[6-(L-prolylamino)benzoic acid] (H₄EDPB). The unique crystal structure of the new compound was established by powder X-ray diffraction. The [Cu₂(EDPB)•H₂O]_n system shows catalytic activity and enantioselectivity in a Henry reaction of p-nitrobenzaldehyde with nitromethane.     

Peculiarities of Catalytic Oxidation of Ethane by Nitrous Oxide on ZSM-5 Type Zeolites Containing Iron Ions in Different Localization Sites

The temperature dependence of the Fe-HZSM-5 activity and selectivity in the process of catalytic oxidation of ethane by the excess of N₂O at 250–350°C exhibits a pronounced hysteresis. The oxidized catalysts free from condensation products are active only in the complete oxidation of ethane. At low temperatures of the reaction of the C₂H₆ + N₂O mixture with the catalyst, coke formation takes place and the coordination state of iron ions differs from the initial sample. Under these conditions, the process of complete oxidation of ethane is essentially suppressed and the process of oxidative dehydrogenation dominates. The catalytic properties of iron-containing zeolites prepared either by direct synthesis or by introduction of iron ions into the cationic positions of H[Al]ZSM-5 are quite similar, because irreversible formation of new iron species considerably different from the initial species takes place during the catalytic reaction on both series of samples. The activity of HZSM-5 containing trace amounts of iron is much lower than that of iron-containing samples.     

New metal organic framework structures based on 2,5-pyridinedicarboxylate ligands and Zn<Superscript>2+</Superscript> ions

Structural characteristics and adsorption properties of new heteroaromatic framework structures based on Zn²⁺ ions and 2,5-pyridinedicarboxylate ligands are investigated. A comparative study of the aromatic framework structure MOF-5 based on Zn₄O clusters and 1,4-benzenedicarboxylate ligands is also performed in order to reveal the effect of the nature of the organic fragment.     

New Bounds and a Generalization for Share Conversion for 3-Server PIR

Private Information Retrieval (PIR) protocols, which allow the client to obtain data from servers without revealing its request, have many applications such as anonymous communication, media streaming, blockchain security, advertisement, etc. Multi-server PIR protocols, where the database is replicated among the non-colluding servers, provide high efficiency in the information-theoretic setting. Beimel et al. in CCC 12’ (further referred to as BIKO) put forward a paradigm for constructing multi-server PIR, capturing several previous constructions for k≥3 servers, as well as improving the best-known share complexity for 3-server PIR. A key component there is a share conversion scheme from corresponding linear three-party secret sharing schemes with respect to a certain type of “modified universal” relation. In a useful particular instantiation of the paradigm, they used a share conversion from (2,3)-CNF over Zm to three-additive sharing over Zpβ for primes p1,p2,p where p1≠p2 and m=p1·p2, and the relation is modified universal relation CSm. They reduced the question of the existence of the share conversion for a triple (p1,p2,p) to the (in)solvability of a certain linear system over Zp, and provided an efficient (in m,logp) construction of such a sharing scheme. Unfortunately, the size of the system is Θ(m2) which entails the infeasibility of a direct solution for big m’s in practice. Paskin-Cherniavsky and Schmerler in 2019 proved the existence of the conversion for the case of odd p1, p2 when p=p1, obtaining in this way infinitely many parameters for which the conversion exists, but also for infinitely many of them it remained open. In this work, using some algebraic techniques from the work of Paskin-Cherniavsky and Schmerler, we prove the existence of the conversion for even m’s in case p=2 (we computed β in this case) and the absence of the conversion for even m’s in case p>2. This does not improve the concrete efficiency of 3-server PIR; however, our result is promising in a broader context of constructing PIR through composition techniques with k≥3 servers, using the relation CSm where m has more than two prime divisors. Another our suggestion about 3-server PIR is that it’s possible to achieve a shorter server’s response using the relation CSm′ for extended Sm′⊃Sm. By computer search, in BIKO framework we found several such sets for small m’s which result in share conversion from (2,3)-CNF over Zm to 3-additive secret sharing over Zpβ′, where β′>0 is several times less than β, which implies several times shorter server’s response. We also suggest that such extended sets Sm′ can result in better PIR due to the potential existence of matching vector families with the higher Vapnik-Chervonenkis dimension.     

Study of the catalytic properties of pentasil-containing composites in transformation of hydrocarbons 4. Formation of products of condensation during oligomerization and aromatization of ethylene on the pentasil-aluminum oxide system

The process of formation of products of condensation (PC) during oligomerization (280°C) and aromatization (500°C) of ethylene in the presence of H-pentasil (HTsVM)--Al₂O₃ was studied by IR spectroscopy, DTA, DTG, and chemical analysis. The mutual effect of the components of the composite on the formation of PC in aromatization of C₂H₄ was detected. PC are formed with the participation of acid sites both inside the channels and on the outer surface of the zeolite. Three types of PC were found: linear polyene structures with C/H=0.8 (oligomerization), aromatic structures with C/H=1.5 (aromatization on HTsVM), and crosslinked polyene structures with C/H=2.45 (aromatization on Al₂O₃). The composition and structure of the PC formed on HTsVM during transformations of ethylene are a function of the molecular-sieve properties of the pentasil and the experimental conditions.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1244–1250, June, 1990.