A series of alumina-based catalysts containing from 0.004 to 0.01 wt% of palladium were prepared via laser electrodispersion and impregnation methods. Three alumina modifications, gamma-Al2O3, theta-Al2O3, and alpha-Al2O3, were used as supports. In the case of the laser electrodispersion method, Pd particles of 2.5 nm in size were evenly distributed on the outer surface of the alumina grains. Contrarily, the impregnation procedure provided the distribution of Pd throughout the whole volume of the support. The catalytic properties of the prepared samples were studied in an acetylene hydrogenation reaction. As found, the catalysts prepared by laser electrodispersion possess a slightly lower activity along with a higher selectivity compared to the impregnated ones. The phase modification of alumina was found to affect the catalytic behavior noticeably. Thus, a decrease in acetylene conversion and an increase in ethylene selectivity were observed for the following order: theta-Al2O3 > gamma-Al2O3 > alpha-Al2O3. The main factors defining the efficiency of the catalysts are metal-support interactions, electronic state, and dispersion and distribution of Pd on the alumina surface. The strongest metal-support interaction was observed for the Pd/theta-Al2O3 sample prepared by laser electrodispersion. This sample has the highest content of Pd2+ species and exhibits high activity but low selectivity to ethylene. In the case of the alpha-Al2O3 support, Pd particles are located close to each other on the outer surface and, therefore, undergo fast deactivation. The X-ray photoelectron spectroscopy data revealed the carbon accumulation during the reaction for all the studied samples.

Preferential oxidation of carbon monoxide (CO-PROX) in H2-rich mixture is an effective way of hydrogen purification for fuel cells. High-performance PtCo/ZSM-5 catalysts with reduced Pt loading for this process were prepared using polynuclear platinum acetate complex known as platinum acetate blue (PAB) of the empirical formula Pt(CH3COO)2.5 as a novel precursor. The impregnation of HZSM-5 (Si/Al = 15 and 28) with PAB and its decomposition at 200 °C resulted in the stabilization of highly dispersed Pt0 and PtOx species on the zeolite surface. The catalytic properties were improved by the addition of Co(CH3COO)2 followed by calcination at 450 °C. Produced materials were studied by SEM, TEM, EDX, XPS, and DRIFTS methods and tested in a CO-PROX reaction. The relationship between the synthesis conditions, structure, and catalytic behavior of composites is discussed in this paper. The synergistic effect of Pt and Co was observed when they both were located together in zeolite channels. The Pt-Co interaction provides new active catalytic sites and prevents platinum aggregation during the process. Due to this, the 100% CO conversion in the wide temperature range from 50 to 130 °C is achieved for PtCo/ZSM-5 catalysts (Si/Al = 15), which is the best result compared to low-loaded Pt catalysts prepared with traditional precursors.

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH3COO)2 impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N2 sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H2-rich mixture (1%CO + 1%O2 + 49%H2 + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts.

Platinum particles of 1.7 nm size were deposited on the external surface of HZSM-5 zeolites with Si/Al = 15, 28, and 40 using laser electrodispersion (LED) method. The obtained materials with low Pt loading (0.01–0.05 wt.

The influence of the synthesis conditions on the performance of Pd–Cu ethanol-to-butanol conversion catalysts was studied. The optimum conditions for forming the most active system 0.2%Cu/0.3%Pd/Al 2 O 3 are as follows: sample synthesis by Al 2 O 3 impregnation from aqueous solutions of Pd and Cu nitrates; deposition of the metal precursors in succession; total content of Pd and Cu in the sample 0.5 wt %; Pd : Сu molar ratio 1 : 1; catalyst reduction temperature 200 ○ С. As shown by TEM, XPS, TPD-NH 3 , TPR-H 2 , XRD, and N 2 adsorption, the surface of the most active catalyst contains Pd 0 Cu 0 particles with the mean size of 4 ± 2 nm. The bimetallic particles are an alloy with the fcc structure and Pd : Cu ratio of 40 : 60. At 275 ○ C, the performance of 0.2%Cu/0.3%Pd/Al 2 O 3 is 182 × 10 –4 mol h –1 g –1 . The value obtained is higher by several orders of magnitude than the performance of the reference catalysts M 1 /Al 2 O 3 (M 1 = Fe, Ni, Co) and by an order of magnitude than that of the reference catalysts M 2 /Al 2 O 3 (M 2 = Ru, Rh, Pt, Pd, Pt–Re, Ni–Mo).

Small amounts of nearly 2-nm Pd nanoparticles (0.01–0.03 wt.%) were deposited onto the surface of the ZSM-5 and BEA zeolites by laser electrodispersion. Materials thus prepared were studied by low-temperature nitrogen adsorption, thermo-programmed desorption of ammonia, transmission electron microscopy, and X-ray photoelectron spectroscopy. They were also tested in total catalytic oxidation of CO and CH4. It was demonstrated that the oxidation state of Pd and the character of distribution of isolated metal particles or their aggregates over the external surface or in the bulk of the zeolite is affected by the palladium content and by the zeolite nature. The activity of the Pd/ZSM-5 catalysts decreases with increasing Si/Al ratio of the zeolite and depends on the oxidation state of the metal. In the most active catalysts 65–75% of Pd occur as metal, whereas 35–25% make up oxidized palladium. The oxidation of carbon monoxide on the ZSM-5 catalyst (Si/Al = 15, 0.01 wt.% Pd) whose surface is uniformly covered with isolated Pd nanoparticles begins at 90 °C, which is 70–80 °C lower compared to CO oxidation on other Pd-modified ZSM-5 and BEA zeolites containing aggregates of palladium nanoparticles.

The present study investigates the regularities in the conversion of ethanol and water/ethanol mixtures in the presence of Au–M/MFI/Al2O3 modified zeolite catalysts, where M = Cu, Ni, and Pd. The conversion products of ethanol, fusel oils, and of a model ethanol/acetone/1-butanol (ABE) mixture were investigated in detail. Transmission electron microscopy (TEM) revealed that supported metal particles mostly aggregate into bimetallic clusters 8–15 nm in size. The variations in product selectivity were found to be caused by coking and, therefore, by a declining concentration of acid sites on the catalyst surface.

BACKGROUND Palladium particles with a size of 2 nm were obtained by laser electrodispersion (LED) and used to prepare the Pd-ZnHZSM-5(LED) catalyst (Pd = 0.0005 wt%). The deposition of the LED palladium particles on the surface of ZnHZSM-5 provided a high dimethyl ether (DME) conversion into liquid hydrocarbons; the percentage of the unreacted intermediate (methanol) decreased by an order of magnitude and the selectivity for i-alkanes increased (more than 80 wt%). The Pd-ZnHZSM-5(LED) catalyst showed higher activity and selectivity than the traditional Pd-ZnHZSM-5 catalyst (impregnation). RESULTS The features of the catalytic action of Pd-ZnHZSM-5(LED) are associated with the high density of nanosized Pd-0 and Pd2+ phases on the ZnHZSM-5 surface. The LED particles are immersed in the surface of the zeolite to a maximum depth of 0.5 nm and do not penetrate deep into the pores of the zeolite. In Pd-ZnHZSM-5(LED), the zinc sites and palladium sites are separate. On Bronsted acid sites and zinc sites in the micropores of the zeolite occure target reactions. Part of arenes and unreacted alkenes exit the pores of zeolite are hydrogenated on the palladium. The product obtained on Pd-ZnHZSM-5(LED) is characterized by a high content of i-alkanes (more than 80 wt%) and a low content of arenes (no more than 5 wt%). CONCLUSION The results demonstrate the high promise of the LED method for the preparation of high-performance catalysts with ultra-low content of noble metal for conversion of oxygenates to synthetic liquid hydrocarbons with a high yield of i-alkanes and low yield of arenes. (c) 2022 Society of Chemical Industry (SCI).

Film photoanodes were made from nanocrystalline TiO2 doped with Bi3+ ions at a concentration of 0.13-3.09 at. %, and their activity towards photoelectrocatalytic oxidation of methanol was studied. It was shown that with a decrease in the Bi content, the photoelectrocatalytic activity of film electrodes gradually increases both when illuminated with monochromatic light (lambda = 461 nm, power of 10 mW cm(-2); lambda = 369 nm, power of 7.5 mW cm(-2)) and when illuminated by a solar simulator with a power of 1 sun (100 mW cm(-2)). It was shown that a decrease in the Bi content leads to a decrease in the recombination losses and to an increase in the efficiency of the transfer of holes involved in the photoelectrocatalytic oxidation of methanol. As a result, doping of TiO2 with an optimal amount of Bi (0.13 at. %) provides selective electrocatalytic oxidation of methanol at the photoanode.

A Pd/Al2O3 catalyst (Pd = 0.1 wt%) for ethanol conversion to butanol deactivates within 10 h of service, despiteits high initial activity at 275°C. Probable deactivation mechanisms wereexplored, including poisoning ofPd/Al2O3 due to adsorption ofby-products on Pd, sintering of Pd phases, leaching of Pd from the catalyst,changes in the Pd electronic state, changes in the catalyst’s porous structure,and blockage of Al2O3 activesites. The Pd/Al2O3 deactivationwas found to be mainly caused by CO molecules that evolved during sidereactions. These molecules can either block Pd active sites due to the formationof strong Pd–CO complexes, or enter a CO disproportionation reaction to formcarbon deposits on Pd phases. The knowledge gained from this study can be usedfor the targeted modification ofPd/Al2O3 and the creation ofselective systems operating stably in the presence of by-products.

Using a combination of physicochemical methods, such as TEM, SEM, EDS, XPS, NH3–TPD, and N2 adsorption, the study investigates the structure of a number of supports (Al2O3, SiO2, TiO2, ZrO2, and C) and of Au/support catalyst samples (Au = 0.5%). The concentration of highly active 2–4 nm gold particles in Au catalysts is influenced by the support’s texture; this concentration increases in the following order: Au/TiO2 < Au/ZrO2 < Au/C < Au/SiO2 << Au/Al2O3. The acidity of Au catalysts is influenced by the support’s nature; this acidity decreases in the following order: Al2O3 > TiO2 > ZrO2 > SiO2 >> Au/C. At 275°C, a carbon support is inactive in ethanol conversion to butanol. In the presence of oxide supports, the target reaction occurs at a relatively low rate by a bimolecular condensation mechanism. Over Au/Al2O3, Au/SiO2, Au/TiO2, or Au/ZrO2, the reaction occurs more rapidly by an aldol condensation mechanism. At an ethanol conversion of 14–18%, the butanol selectivity increases in the following order: Au/C(0) << Au/SiO2 (0.4%) < Au/ZrO2 (1.5%) < Au/TiO2 (2%) << Au/Al2O3 (78%). The high efficiency of Au/Al2O3 stems from the high density of the Aln+–O2– sites located on the support’s surface, and of the coordination-unsaturated Au0(KH) atoms located on the surface of 2–4 nm gold particles.

Pd/Al2O3 and Pd–M/Al2O3 catalysts (M = Au, Ag, Cu, Ce, Fe, Ni, Co, Zn) were obtained by ion exchange and impregnation. Pd/Al2O3 had high initial activity in the conversion of ethanol into α-alcohols, but lost 90% of its activity after 10 h of operation because of deactivation caused by the chemisorption of the by-product (CO) on Pd atoms. Modification of Pd with gold or silver led to an increase in the rate of Pd deactivation. As a result, the Pd–Au and Pd–Ag systems were less active and stable. In contrast, the Pd–Fe, Pd–Co, Pd–Ni, Pd–Cu, Pd–Zn, and Pd–Ce systems exhibited higher resistance to CO poisoning than Pd and demonstrated high activity and stability. The observed tendencies in the catalytic action of the mono- and bimetallic systems were explained within the framework of the d band model proposed by Hammer and Norskov. Pd–Cu/Al2O3 was most effective in the target process; it is not poisoned by CO and allows ethanol conversion into α-alcohols at 95% selectivity, while the time of its stable operation is at least 100 h. The structure of the Pd–Cu catalytic system was studied by TEM, EDA, XPS, TPR-H2, and TPD-NH3. A model of active catalyst sites was proposed.

This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O-2 ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O-2 = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O-2 = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt-0 dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O-2 ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle support interactions.

PdCu/Al2O3 (Pd = 0.1 wt.%, Cu = 0.1 wt.%) catalyst and its monometallic analogues (Pd/Al2O3 and Cu/Al2O3) were prepared by combination of deposition-precipitation and impregnation methods. The structure of the catalysts was studied by means of XRD, TEM, EDS, TPD-NH3, and DRIFTS. In a standard run (275 White circleC, 5 h), Cu/ Al2O3 converts 11 % of ethanol to alpha-alcohols with 0.6 % selectivity, whereas Pd/Al2O3 converts 24 % of ethanol to alpha-alcohols with 70 % selectivity. The high performance of Pd/Al2O3 was attributed to the catalysis on the Pd degrees Al2O3 interfaces. After 3 sequential runs, the activity of Pd/Al2O3 decreases by 98 %. It was explained by blocking of Pd degrees sites in Pd/Al2O3 by CO molecules produced in side reactions. Modification of Pd/Al2O3 with Cu species results in the formation of PdCu/Al2O3 catalyst containing PdCu alloy particles with the size of 4 nm. This leads to an increased durability of bimetallic sample, because of suppressing CO sorption on Pd degrees sites in alloy particles. As a result, for the PdCu/Al2O3 catalyst, sustained and high conversion (41 %) accompanied by high selectivity to alpha-alcohols (91 %) was observed in 20 sequential runs.

A new approach was developed for the formation of an adsorbent from solid residual products of carbon dioxide reforming of Fe-containing lignin. The key stages of this approach are: (1) etching of residual products with dilute HCL; (2) carbon dioxide treatment with microwave plasma induction at 950-1000 degrees C; and (3) thermal shock. The sequential application of procedures (1)-(3) to the residual products of carbon dioxide reforming of Fe-containing lignin affords a carbon adsorbent with a specific surface area of similar to 578 m(2)/g and comparable volumes of micro- and mesopores.

The structure of Fe-containing components of the carbon adsorbent preparedfrom the residue after carbon dioxide lignin reforming stimulated by microwaveradiation was studied before and after the m-cresol sorption. As shown by X-ray photoelectron spectroscopy(XPS), the prevalent state of iron in the samples isFe3+. The revealed “apparent decrease in the ironcontent” after the adsorbent treatment with cresol is due to the formation ofsurface complexes partially absorbing the emitted photoelectrons. The Mössbauerspectra show that the iron-containing phase of the initial adsorbent contains afraction of Fe0 atoms (≈7%), which are oxidized from0 to 3+ oxidation state upon m-cresoladsorption. This result can be attributed to the occurrence of reactionsyielding surface iron alcoholates.