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Abstract A study of a series of single-atom-alloy catalysts Pd1Ag3/Al2O3, Pd1Ag3/CeO2–Al2O3, and Pd1Ag3/CeO2–ZrO2 in the selective hydrogenation of diphenylacetylene (DPA) showed a significant (five-fold) increase in activity for the PdAg3/CeO2–ZrO2 sample in comparison with that of Pd1Ag3/Al2O3. It was especially noted that the increase in activity was not accompanied by a decrease in the selectivity for the target product. This catalytic behavior can be explained by two factors: (1) a more than twofold increase in the dispersity of the PdAg3/CeO2–ZrO2 catalyst and (2) a change in the electronic state of the nanoparticles, as determined from the results of an IR-spectroscopic study of adsorbed CO. The retention of the high selectivity of the synthesized catalysts indicated the stability of the structure of Pd1 monoatomic sites in the catalysts prepared by deposition on Ce-containing supports, which was also confirmed by the IR spectroscopy of adsorbed CO. The experimental results indicate that Ce-containing supports are promising for the synthesis of catalysts for the selective hydrogenation of substituted alkynes.

5-Methyl-4-[(propylsulfanyl)methyl]-2,4-dihydro-3H-pyrazol-3-one was shown to inhibit the radical-chain peroxidation of 1,4-dioxane, ethylbenzene, and methyl oleate. One peroxyl radical is trapped by each (propylsulfanylmethyl)-substituted 2,4-dihydro-3H-pyrazol-3-one molecule. The reaction rate constant of the compound with a peroxyl radical depends on the structure of the latter and decreases in the series: peroxyl radical of 1,4-dioxane, ethylbenzene, and methyl oleate (k7 × 104, L mol –1 s–1, 333 K: 5.7, 4.1, 1.1). The reason for the observed dependence was discussed.

The properties of the FeBeta zeolite catalyst, MnCe/FeBeta composite catalyst, and FeBeta∥MnCe/FeBeta dual-zone catalytic system were studied in the selective catalytic reduction of nitrogen oxides with ammonia. The combination of the low-temperature (MnCe/FeBeta) and high-temperature (FeBeta) catalysts makes it possible to significantly improve the efficiency of NOx removal in a wide temperature range (200–500 °C) in the presence of the FeBeta∥MnCe/FeBeta system. It was found that this system also demonstrates high activity in the catalytic oxidation of residual ammonia retaining high selectivity in molecular nitrogen formation even under ammonia excess conditions (NH3: NO > 1).

The structure of Pd–Ag/Al2O3 samples with different Ag/Pd ratios has been studied by a complex of physicochemical methods (H2-TPR, XRD, H2-TPD, TEM). Catalysts have been synthesized by supporting an active component on α-Al2O3 and γ-Al2O3. X-ray diffraction analysis has revealed the formation of a Pd–Ag substitutional solid solution with a face-centered cubic crystal lattice owing to alloying of the Pd and Ag components. An increase in the Ag content in the composition of bimetallic nanoparticles hinders the formation of palladium hydride (PdHx), which is completely suppressed at a ratio of Ag/Pd > 0.5. Infrared spectroscopy of adsorbed CO has revealed the formation of single-atom Pd1 sites on the surface of supported Pd–Ag bimetallic nanoparticles isolated from each other by silver atoms. Analysis of the structural stability of isolated Pd1 sites has shown that, under conditions of CO adsorption at 150°C, the stability of the sites can be provided by an increase in the Ag/Pd ratio to ≥2.

Novel one-pot synthesis of trans-stilbene comprises hydrogenation of diphenylacetylene into cis-stilbene followed by its hydroisomerization, over the catalyst being intermetallic PdxIny/Al2O3 system with isolated single-atom Pd1 sites. The hydroisomerization rate in the process is comparable or exceeds the over-hydrogenation into 1,2-diphenylethane thus providing 76% yield of trans-stilbene in the case of Pd2In3/Al2O3 catalyst. This result presumably stems from the formation of ordered single-atom Pd1 sites with favorable hydroisomerization ability on the surface of PdxIny catalysts.

Local structure of Pd1 single sites on the surface of Pd1In1 intermetallic nanoparticles supported on α-Al2O3 was investigated by the combination of CO-DRIFTS spectroscopy and DFT. CO-DRIFTS spectra of PdIn/Al2O3 catalyst exhibit only one asymmetric absorption band of linearly adsorbed CO comprising two peaks at 2065 and 2055 cm−1 attributable to CO molecules coordinated to Pd1 sites located at (110) and (111) facets of PdIn nanoparticles. The absence of bridged or hollow-bonded CO bands indicates that multipoint adsorption on PdIn nanoparticles is significantly hindered or impossible. DFT results show that on (110) facet multipoint CO adsorption is hindered due to large distance between neighboring Pd atoms (3.35 Å). On (111) facet multipoint CO adsorption on surface palladium atoms is impossible, since adjacent Pd atoms are located below the surface plane.

A series of oxidative treatments of PdIn-supported intermetallic nanoparticles at different temperatures were performed. The bulk and surface structure of catalyst during phase transformation was investigated by bulk- and surface-sensitive techniques (in situ XAFS, DRIFTS of adsorbed CO). It was found that comparison of palladium and indium fractions in bulk and on the surface suggests the formation of a «core-shell» structure. According to obtained results, the core consists of In-depleted intermetallic compound or inhomogeneous bimetallic phase with the inner core of metallic Pd, when a mixture of indium oxide, metallic palladium and small part of PdIn is present on the surface.

The structure and catalytic characteristics of a bimetallic catalyst containing Pd1In1 nanoparticles deposited on the surface of γ-Al2O3 were studied. The formation of intermetallic nanoparticles was determined by X-ray diffraction analysis and confirmed by X-ray photoelectron spectroscopy and IR spectroscopy of adsorbed CO. In the hydrogenation of acetylene in excess ethylene, PdIn/Al2O3 had significantly higher selectivity of ethylene formation (~86%) than monometallic Pd/Al2O3 (~35%). The high selectivity of PdIn/Al2O3 is explained by two factors: (1) the formation of monatomic Pd1 sites isolated from one another by In atoms and (2) the change in the electronic state of Pd atoms in the intermetallic nanoparticles.

The structure and catalytic properties of a bimetallic Pd–Ag/α-Al2O3 catalyst are studied in the liquid-phase hydrogenation of substituted internal and terminal alkynes using diphenylacetylene, phenylacetylene, 1-phenyl-1-propyne, and 1-phenyl-1-butyne as sample alkynes. IR spectroscopy of adsorbed CO, X‑ray diffraction (XRD), and electron microscopy were used to show that the active sites on the Pd–Ag nanoparticle surface are Pd1 sites. The synthesized Pd–Ag/α-Al2O3 catalyst shows a much higher selectivity in the hydrogenation of internal symmetric and asymmetric alkynes compared to the monometallic Pd/α‑Al2O3 sample. Also, it was found in the hydrogenation of diphenylacetylene and 1-phenyl-1-propyne on Pd–Ag/α-Al2O3 that the rate of the stage of desired olefin hydrogenation substantially decreases, which favors the kinetic control of the process.

A dual-bed catalytic system has been developed for the complex after treatment of diesel engine exhaust gases comprising nitrogen oxides, CO, hydrocarbons, and residual NH3 (NH3-slip) within wide temperature range. The system demonstrates effective NOx abatement at 200–500 °C. The upstream bed (FeBeta) is responsible for the selective catalytic reduction of NOx by ammonia (NH3-SCR) above ~ 300 °C, while the downstream bed ([Mn–Ce/CeO2–ZrO2 + FeBeta] combined catalyst) provides effective NOx abatement below 300 °C and total oxidation of CO, hydrocarbons, and NH3-slip.

Volatile organic compounds (VOCs) have a negative effect on both humans and the environment, therefore, it is crucial to minimize their emission. The conventional solution is the catalytic oxidation of VOCs by air, however, in some cases this method requires relatively high temperatures. Thus, the oxidation of short-chain alkanes, which demonstrate the lowest reactivity among VOCs, starts at 250–350 °C. This research deals with the ozone catalytic oxidation (OZCO) of alkanes at temperatures as low as 25–200 °C using an alumina-supported manganese oxide catalyst. Our data demonstrate that oxidation can be significantly accelerated in the presence of a small amount of O3. In particular, it was found that n-C4H10 can be readily oxidized by an air/O3 mixture over the Mn/Al2O3 catalyst at temperatures as low as 25 °C. According to the characterization data (SEM-EDX, XRD, H2-TPR, and XPS) the superior catalytic performance of the Mn/Al2O3 catalyst in OZCO stems from a high concentration of Mn2O3 species and oxygen vacancies.

Solid-state ion exchange in mixtures of copper oxides and zeolites can occur at temperatures as low as 200–250 °C in the presence of ammonia (NH3-SSIE), thus providing a low-temperature method to activate zeolites for selective catalytic reduction nitrogen oxide (NH3-SCR). The ammonia induced solid-state ion exchange process is studied in more detail, by monitoring the development of NH3-SCR activity with duration of NH3-SSIE, formation of a mobile linear [Cu(NH3)2]+ complex with X-ray spectroscopy, and the transfer of Cu to the zeolite by XRD, and evaporation of copper(I)-oxide by TGA. We find that the linear [Cu(NH3)2]+ complex is formed in mixtures of copper-oxide and *BEA and CHA zeolites upon exposure to ammonia. Increasing the temperature for NH3-SSIE to well above 300 °C leads to a less efficient Cu-transfer. This indicates that the [Cu(NH3)2]+ complex is crucial for the NH3-SSIE process. The non-monotonous development of NOx conversion and N2O yield with duration of NH3-SSIE is probably due to an initial enrichment of Cu in the outer shell of the zeolite crystals. We also show that the presence of H+ or NH4+-ions in the zeolite are necessary for the NH3-SSIE, and that the transfer of Cu from the Cu-oxides to the zeolites most likely occurs via a surface diffusion process.

FeBeta||Mn–Ce/FeBeta catalyst was prepared by coating cordierite monolith with FeBeta zeolite followed by an impregnation of its downstream part by Mn–Ce solution. The resulting dual-zone catalyst demonstrates improved catalytic performance in the selective catalytic reduction of NOx by NH3 (NH3-SCR) as compared to the parent Fe-Beta. The catalyst exhibits 80–90% NOx conversion and 100% selectivity to N2 within wide temperature ranges: 180–500 °C (at GHSV = 18,000 h−1) and 260–500 °C (at GHSV = 54,000 h−1). Moreover, the dual-zone catalyst provides favorable NH3-slip removal efficiency even at NH3/NO = 1.60.

The structure and catalytic characteristics of a series of Pd–Cu/α-Al2O3 catalysts with Pd: Cu ratio varied from Pd1–Cu0.5 to Pd1–Cu4 were studied. The use of α-Al2O3 with a small surface area (Ssp = 8 m2/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd0 and Cu0 nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.

The effect of palladium segregation was studied which resulted from the effect of CO and O2 on the surface structure and catalytic characteristics of the Pd–Ag2/Al2O3 catalyst. The IR-spectroscopic study of adsorbed CO showed that Pd1 centers isolated from each other by silver atoms predominated on the surface of reduced Pd–Ag2/Al2O3, as evidenced by the almost complete absence of absorption bands typical for the multicentred CO adsorption. In the course of catalyst treatment with CO and O2, the intensity of absorption bands characteristic of the multicenter CO adsorption considerably increased due to the transformation of a portion of monatomic Pd1 centers into multiatomic Pdn ones as a result of the surface segregation of Pd. In this case, a substantial increase in the catalyst activity in the liquid-phase hydrogenation of diphenylacetylene was observed. It was established that, after treatment with CO, the catalyst selectivity for the formation of a target olefin (stilbene) remained almost constant, whereas the treatment with O2 led to a decrease in the selectivity because of more considerable surface modification.

A treatment of PdAg3/Al2O3 catalyst with CO at 250 °C enhanced its activity towards the selective C2H2 hydrogenation without any noticeable losses of C2H4 selectivity. The CO-DRIFTS and XPS data acquired in situ have indicated that the observed effect arises from Pd surface segregation induced by the CO adsorption and partial transformation of isolated surface Pd1 active sites into Pd2 dimers. The catalytic performance of PdAg3/Al2O3 was found to be similar or even better as compared to the best reported catalysts.

Palladium catalysts on various types of supports were studied in the liquid-phase hydrogenation of diphenylacetylene. Samples of Pd/SiO2–Al2O3, Pd/MgAl2O4, Pd/Al2O3, and Pd/TiO2 were characterized by the chemisorption of the CO and IR spectroscopy of adsorbed CO. The use of n-hexane as the solvent increases the reaction rate, which can be explained by the better solubility of hydrogen in the liquid phase. It is established that the acid–base properties of the support do not affect the activity and selectivity of the catalysts in the reaction under study. However, they alter the electronic state of palladium. According to the catalytic tests, Pd/TiO2 has the highest activity (turnover frequency) and selectivity to alkene. The comparison of the obtained catalytic data and the results of IR spectroscopy made it possible to conclude that this is due to the electron density redistribution between the palladium and TiO x particles, which is caused by the strong metal–support interaction.

The hydroisomerization of a cis-isomer to produce a trans-isomer on Rh, Pd, Pt, Ru, and Ir/α-Al2O3 catalysts is studied. It is shown that Rh and Ru catalysts on which the hydroisomerization reaction mostly takes place exhibit the most favorable characteristics, whereas on the other metals, the main route is the hydrogenation reaction. Rh/α-Al2O3 is the optimum catalyst, since it has much higher activity than Ru/α-Al2O3. It is found that the increased selectivity of the trans-isomer formation is facilitated by a decrease in the hydrogen pressure and by an increase in the substrate concentration. The maximum selectivity is achieved when the reaction is carried out in nonpolar n-hexane and toluene, whereas in the case of the more polar tetrahydrofuran (THF), dimethylformamide (DMFA), and methanol both the reaction rate and the selectivity of the trans-isomer formation decline.

A comparative study of the catalytic characteristics of monometallic Pd/α-Al2O3 and bimetallic Pd–Zn/α-Al2O3catalysts in the liquid-phase hydrogenation of structurally different substituted alkynes (terminal and internal, symmetrical and asymmetrical) was carried out. It was established that an increase in the reduction temperature from 200 to 400 and 600°C led to a primary decrease in the activity of Pd–Zn/α-Al2O3 due to the formation and agglomeration of Pd1–Zn1 intermetallic nanoparticles. The Pd–Zn/α-Al2O3 catalyst containing Pd1–Zn1 nanoparticles exhibited increased selectivity to the target alkene formation, as compared with that of Pd/α-Al2O3. Furthermore, the use of the Pd–Zn/α-Al2O3 catalyst made it possible to more effectively perform the kinetic process control of hydrogenation because the rate of an undesirable complete hydrogenation stage decreased on this catalyst.

The in situ DRIFT-CO and XPS data demonstrated that the mild oxidation of PdIn intermetallic nanoparticles results in the partial oxidation of an In component and the trans-formation of isolated Pd1 sites to Pdn multiatomic ones thus enhancing PdIn activity in the liquid-phase hydrogenation of diphenylacetylene without sacrificing the alkene selectivity.

The catalytic performance of 3 wt% Pd–Cu/Al2O3 containing bimetallic alloy Pd–Cu nanoparticles strongly depends on the Pd/Cu ratio in the cross-coupling of phenylacetylene with phenyl iodide, and a maximum activity is attained at Pd/Cu = 1:2.

The complex characterization of a PdZn /Al2O3 catalyst by XPS, XRD, TEM and H2-TPD techniques revealed the route of solid-state alloy → intermetallics transformation. The influence of this transformation on the performance of PdZn /Al2O3 in the liquid-phase hydrogenation of diphenylacetylene was estimated.

Phase transformations of a newly synthesized heterobimetallic ZnPt(OOCMe)4(H2O)(MeCOOH)2 acetate in a chemically reductive atmosphere at mildly elevated temperatures are thoroughly studied in order to optimize conditions for the formation of nanostructured PtZn intermetallic compound. According to XAFS and XRD data, the first stage of reductive thermolysis is the reduction of the noble metal, while zinc remains in an oxygen environment. At the second stage the reduction of Zn and the formation of the bimetallic solid solution with the fcc lattice occur. It is shown that recrystallization of solid solution to ordered PtZn intermetallic compound with the tetragonal structure occurs in a narrow temperature range of 250–275 °C. Based on these results, the optimum reduction temperature for the preparation of supported bimetallic Pt–Zn/Al2O3 catalyst was determined to be 300 °C. Results of catalytic tests of the supported material are reported.

Catalytic performance of Pd1Ag3/Al2O3 single-atom alloy (SAA) catalyst was studied in liquid-phase hydrogenation of diphenylacetylene (DPA) and compared with the performance of the reference monometallic Pd/Al2O3. Formation of SAA structure in Pd1Ag3/Al2O3 was confirmed by FTIR CO technique. It was found that Pd1Ag3/Al2O3 single-atom alloy catalyst exhibits excellent selectivity in diphenylethene (stilbene) (ca. 98 %), which remains constant over a wide range of DPA conversions (0–95%), while over Pd/Al2O3 selectivity decreases steadily with the increase in DPA conversion. It is remarkable that the selectivity of Pd1Ag3/Al2O3 depends neither on hydrogen pressure (5–15 bar), nor on DPA concentration (0.0262 – 0.159 mol/l). In contrast, over the reference Pd/Al2O3 selectivity tends to decrease with increasing P(H2) and decreasing DPA concentration. The proposed reaction network comprises hydrogenation of DPA in a parallel formation of cis and trans-stilbene with following hydrogenation to bibenzyl and direct formation of the latter from the initial DPA. The calculations clearly shows the capability of the kinetic model to describe the experimental dependencies for Pd1Ag3 single-atom catalyst in an excellent way with the degree of explanation equal to ca. 99 %.

A comparative catalytic study of Pd–Ag bimetallic catalysts and the commercial Lindlar catalyst (Pd–Pb/CaCO3) has been carried out in the hydrogenation of phenylacetylene (PA) and diphenylacetylene (DPA). The Pd–Ag catalysts have been prepared using the heterobimetallic complex PdAg2(OAc)4(HOAc)4 supported on MgAl2O4 and aluminas (α-Al2O3 and γ-Al2O3). Physicochemical studies have demonstrated that the reduction of supported Pd–Ag complex with hydrogen results in homogeneous Pd–Ag nanoparticles. Equal in selectivity to the Lindlar catalyst, the Pd–Ag catalysts are more active in DPA hydrogenation. The synthesized Pd–Ag catalysts are active and selective in PA hydrogenation as well, but the unfavorable ratio of the rates of the first and second stages of the process makes it difficult to kinetically control the reaction. The most promising results have been obtained for the Pd–Ag2/α-Al2O3 catalyst. Although this catalyst is less active, it is very selective and allows efficient kinetic control of the process to be carried out owing to the fact that, with this catalyst, the rate of hydrogenation of the resulting styrene is much lower than the rate of hydrogenation of the initial PA.

The formation of Pd–Ag nanoparticles deposited from the heterobimetallic acetate complex PdAg2(OAc)4(HOAc)4 on α-Al2O3, γ-Al2O3, and MgAl2O4 has been investigated by high-resolution trans-mission electron microscopy, temperature-programmed reduction, and IR spectroscopy of adsorbed CO. The reduction of PdAg2(OAc)4(HOAc)4 supported on γ-Al2O3 and MgAl2O4 takes place in two steps (at 15–245 and 290–550°C) and yields Pd–Ag particles whose average size is 6–7 nm. The reduction of the Pd–Ag catalyst supported on α-Al2O3 occurs in a much narrower temperature range (15–200°C) and yields larger nanoparticles (~10–20 nm). The formation of Pd–Ag alloy nanoparticles in all of the samples is demonstrated by IR spectroscopy of adsorbed CO, which indicates a marked weakening of the absorption band of the bridged form of adsorbed carbon monoxide and a >30-cm–1 bathochromic shift of the linear adsorbed CO band. IR spectroscopic data for PdAg2/α-Al2O3 suggest that Pd in this sample occurs as isolated atoms on the surface of bimetallic nanoparticles, as is indicated by the almost complete absence of bridged adsorbed CO bands and by a significant weakening of the Pd–CO bond relative to the same bond in the bimetallic samples based on γ-Al2O3 and MgAl2O4 and in the monometallic reference sample Pd/γ-Al2O3.

The formation of Pd–In catalysts synthesized from the heteronuclear acetate complex PdIn(CH3COO)5 was studied by temperature-programmed reduction, electron microscopy, IR spectroscopy of adsorbed CO and hydrogen temperature-programmed desorption (H2-TPD). IR spectroscopy of adsorbed CO and H2-TPD confirmed the formation of bimetallic Pd–In nanoparticles. It was found that the Pd–In nanoparticle surface contains predominantly Pd atoms separated from one another by indium atoms, which is evidenced by the disappearance of the CO band shift resulting from the lateral dipole–dipole interaction between adsorbed CO molecules and by a significant decrease in the band intensity of CO adsorbed in bridged form. Almost complete inhibition of palladium hydride (PdHx) provides additional evidence of the formation of Pd–In bimetallic particles.

Pd–In/Al2O3 and Pd–In/MgAl2O4 catalysts prepared from dinuclear Pd–In acetate complexes were studied in the hydrogenation of alkyne compounds with different structures. The Pd–In catalysts demonstrate high selectivity in the hydrogenation of internal alkynes comparable with that of the Lindlar catalyst. Similar activity/selectivity characteristics are reached at a significantly lower Pd content. For terminal alkynes, the favorable effect of Indium introduction is considerably less pronounced. An analysis of the In effect on the selectivity and the ratio between the rates of the first and second hydrogenation steps suggests that the reaction selectivity is determined to a large extent by a thermodynamic factor (adsorption–desorption equilibrium between the reactants and the reaction products).

Low-temperature NO storage process over Pt/CeO2–ZrO2 was studied in detail by the isothermal adsorption and the temperature-programmed adsorption measurement mimicking cold start of the real diesel engine. Maximal NOx storage capacity determined by saturation of Pt/Ce–Zr at 120 °C approaches ~0.18 mmol/g (8.5 $${\text{g}}_{{{\text{NO}}_{2} }}$$ /kgcat). TPD and in situ FTIR study indicated that NO is stored over catalyst surface as nitrite ( $${\text{NO}}_{2}^{ - }$$ )surf and nitrate ( $${\text{NO}}_{3}^{ - }$$ )surf species. NOx storage capacity was found to be a function of NO inlet concentration in accordance with the relationship: NOstored ~ [NOx,inlet]0.4. CO2 significantly deteriorates NOx storage at 100–200 °C presumably due to formation of surface carbonate species decomposed above 200–250 °C.

NH3–SCR performance of the combined catalyst (CombiCats) prepared by mechanical mixing of CeO2–ZrO2 and H-Beta is studied in details. It was shown, that individual standard SCR activities of CeO2–ZrO2 and H-Beta are negligible, while their mixing results in the significant improvement of NOx conversion. The absence of standard SCR activity of individual components enabled us to estimate the contribution of fast SCR, NO and NH3 oxidation reactions to the overall process on CombiCat. Comparison of catalytic data obtained for layered configurations and CombiCats with various CeO2–ZrO2/H-Beta ratios also allowed us to determine the rate-limiting step and role of each component in the process.

A comprehensive study has been performed on the catalytic properties of composite catalysts [Mn/support + FeBeta] and their individual components (Mn/support and FeBeta) in the selective catalytic reduction of nitrogen oxides and the ammonia oxidation reaction. It has been shown that mixing the oxide component with the zeolite not only leads to an increase in NO x conversion, but also improves the selectivity in the oxidation of residual ammonia, thus making it possible to conduct both processes in a single catalytic unit.

NH3-DeNOx performances of the combined catalysts (CombiCats) prepared by mechanical mixing of RedOx component (CeO2–ZrO2 or Mn–Ce/CeO2–ZrO2) and zeolite component (Fe-Beta, H-Beta, USY, etc.) were studied in details. By comparing DeNOx performances of the CombiCats and their individual components a pronounced synergistic effect was revealed, as evidenced by the improvement of DeNOx activities and selectivities far above performances of the individual components. Significant improvement was observed within 150–250 °C temperature range. Detailed study of a possible origin of the synergistic effect suggested that the improvement of NH3-DeNOx activity can be attributed to the bifunctional mechanism comprising two main stages: (1) 2 NO + O 2 ↔ 2 NO 2 over RedOx component (2) NO + NO 2 + 2 NH 3 → 2 N 2 + 3 H 2 O over zeolite component Remarkably, the synergistic effect was attained by mixing RedOx component with H-Beta possessing negligible activity in Standard SCR but active in Fast SCR. Nevertheless, further research is required for revealing overall reaction network and understanding reaction mechanism responsible for the observed synergy.

The CO-DRIFTS investigation of a Pd–In catalyst obtained via the PdIn(AcO)5 complex showed the presence of single palladium atoms isolated by indium on the surface. A short-time exposure to air under ambient conditions induced the decomposition of the single-atom structure, which can be recovered by mild reduction.

Formation of PdIn intermetallic nanoparticles supported on &alpha, Al2O3 was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and hydrogen temperature-programmed desorption (H2-TPD) methods. The metals were loaded as heterobimetallic Pd(&mu, O2CMe)4In(O2CMe) complex to ensure intimate contact between Pd and In. Reduction in H2 at 200 &deg, C resulted in Pd-rich PdIn alloy as evidenced by XRD and the disappearance of Pd hydride. A minor amount of Pd1In1 intermetallic phase appeared after reduction at 200 &deg, C and its formation was accomplished at 400 &deg, C. Neither monometallic Pd or in nor other intermetallic structures were found after reduction at 400&ndash, 600 &deg, C. Catalytic performance of Pd1In1/&alpha, Al2O3 was studied in the selective liquid-phase diphenylacetylene (DPA) hydrogenation. It was found that the reaction rate of undesired alkene hydrogenation is strongly reduced on Pd1In1 nanoparticles enabling effective kinetic control of the hydrogenation, and the catalyst demonstrated excellent selectivity to alkene.

The liquid-phase hydrogenation of diphenylacetylene over Pd catalysts supported on Al2O3 with different specific surface areas has been investigated. A decrease in the specific surface area of the support leads to a marked increase in the selectivity of the reaction. The observed increase in the selectivity is due to the increase in the size of Pd0 nanoparticles. As a result, the specific rate of triple bond hydrogenation increases over the rate of the undesired hydrogenation of the olefinic intermediate and the efficiency of kinetic control over the selectivity of the overall process is enhanced.

Properties of Pd–Cu/Al2O3 catalysts prepared using PdCu(CH3CO2)4 acetate heteronuclear complexes as precursors in the liquid-phase diphenylacetylene (DPA) hydrogenation have been studied. It has been established that the reaction over the Pd–Cu/Al2O3 catalyst proceeds more selectively than over the commercial Lindlar catalyst; in addition, high activity is achieved at a substantially lower palladium content. The maximum selectivity of DPA hydrogenation is observed with the catalyst reduced in a hydrogen atmosphere without any intermediate calcination that can result in the destruction of the bimetallic acetate complex. FTIR spectroscopy data for adsorbed CO show that the high selectivity of hydrogenation is due to the formation of homogeneous Pd–Cu particles and to the absence of monometallic palladium particles. This can be explained by the retention of the initial complex structure at all of the catalyst preparation stages until the formation of bimetallic particles during hydrogenation.

The formation of a PdCu alloy with an fcc structure in 1% Pd–1.2% Cu2 /Al2O3 (as evidenced by XRD and EXAFS data) significantly improves catalyst selectivity in the semihydrogenation of internal and terminal alkynes, which makes 1% Pd–1.2% Cu2 /Al2O3 a promising alternative to the commercial Lindlar catalyst.

The 1% Pd–1% In / MgAl2O4 catalyst demonstrated excellent selectivity in the semi-hydrogenation of internal 1-phenylprop-1-yne, which exceeded the selectivity of a commercial Lindlar catalyst and reference monometallic 0.5% Pd/MgAl2O4 catalyst due to Pd–In alloy formation.

Pd-In/Al2 O3 single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al2 O3 in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire 1 H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.

The role of nitrate ad-species in H2-assisted SCR over Ag/Al2O3 was compared in NH3-SCR and n-C6H14-SCR processes. It was found that nitrates could be reduced by NH3 or n-C6H14 at similar rates with H2 co-feeding which indicates a common rate-limiting step. However, contributions of surface nitrate reduction to the overall NH3-SCR or n-C6H14-SCR are different as revealed by comparing the rates of nitrate reduction with the rates of steady-state processes. The rate of the steady-state n-C6H14-SCR is virtually identical to the rate of surface nitrate reduction suggesting a significant contribution of the surface nitrates reduction to the overall n-C6H14-SCR process. On the other hand, the steady-state rate of NH3-SCR is by ~15 times higher, which indicates that the reduction of surface nitrates plays a marginal role in the overall NH3-SCR.

Performance of the combined catalysts [CeO2–ZrO2 + FeBETA] and [Mn/CeO2–ZrO2 + FeBETA], prepared by mechanical mixing of the component powders, was studied in soot oxidation and NH3-SCR. [CeO2–ZrO2 + FeBETA] catalyst (with component volumetric ratio of 3/1) demonstrated efficient soot oxidation at 400–450 °C and DeNO x performance similar to that of FeBETA catalyst, despite the fact that the amount of zeolite was reduced by four times indicating a strong synergistic effect between the components. Low-temperature DeNO x performance of the [CeO2–ZrO2 + FeBETA] system can be additionally enhanced by doping the CeO2–ZrO2 with Mn. It was found that NO x conversion over [Mn/CeO2–ZrO2 + FeBETA] at 150–250 °C was steadily improved by increasing the Mn loading, and [5.4 % Mn/CeO2–ZrO2 + FeBETA] attained NO x conversion above 90 % at Treact ~190 °C. Comparative studies of soot oxidation and NH3-SCR over combined catalysts and individual components indicated that the soot oxidation activity is assigned to the soot oxidation over ceria–zirconia component, while enhanced low-temperature SCR performance is a result of a “bi-functional” SCR mechanism comprising NO oxidation to NO2 over CeO2–ZrO2 component followed by fast-SCR over FeBETA.

The activity of 0.25–5% Ag/Al2O3 catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H2 was studied. It was found that, upon the introduction of ∼1000 ppm of H2 into the reaction mixture, the Ag/Al2O3 samples containing 1–2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm of H2, the rate of the selective catalytic reduction of NO x was higher by a factor of 10–13, and the onset temperature of the reaction was lower by approximately 100°C. It was found by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1–2% Ag/Al2O3 catalysts was due to the presence of small Ag δ+ and Ag 0 clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of Ag2O and Ag0, which facilitate the oxidation of n-C6H14, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides.

The efficiency of TiO2 (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O2 + N2 mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO2, NO3−), it is impossible to realize prolonged continuous removal of NOx (NO + NO2) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NOx adsorbed during 2-h-long irradiation. Modification of TiO2 with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO2 and NO3−. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO2. The SPC of the (0.5% Pt)/TiO2 catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt+ and Pt2+, have an approximately 2 times higher SPC than unpromoted TiO2 and ensure a much larger NO2/NO ratio at the reactor outlet. Conversely, the samples reduced in an H2 atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO2 and cause no significant change in the NO2/NO ratio.

The formation of Pd–Zn alloy was revealed in a highly selective Pd–Zn/C catalyst for acetylene hydrogenation prepared via the heterobimetallic PdZn(OAc)4(OH2) complex.

Specific features of the catalytic behavior of supported palladium nanoparticles were analyzed in terms of both the size of the particles and their interaction with the support. The influence of these factors on the activity and selectivity of palladium nanoparticles in carbon-carbon bond hydrogenolysis, hydrogenation of aromatic compounds, olefins, and acetylenes, hydrodechlorination, as well as complete oxidation of organic compounds was discussed. It was shown that the optimal nanoparticle size depends on the type of the reaction and also such factors as the nature of interaction between the nanoparticles and support, absorptivity of the substrates and catalytic reaction products, and electronic and crystal structure of the nanoparticles.

The catalytic properties of new Pd-Zn/Al2O3 catalysts in selective acetylene hydrogenation in an acetylene-ethylene mixture at 30–120°C and atmospheric pressure are reported. The catalysts prepared from the bimetallic complex Pd-Zn(OOCMe)4(OH2) are much more selective than the catalysts prepared by simultaneously supporting the homonuclear complexes Pd3(OOCMe)6 and Zn(OOCMe)2 · 2H2O. It is demonstrated by diffuse reflectance IR spectroscopy of adsorbed CO that the heat treatment of the supported bimetallic complex at 250°C in flowing H2 yields a Pd-Zn alloy on the surface. It is this alloy that ensures the high selectivity of the Pd-Zn/Al2O3 catalysts.