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).

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).

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.

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.

The features of the liquid-phase hydrogenolysis of glycerol to 1,2-propylene glycol over Cu/Al2O3 catalysts (Cu = 2–80 wt %) and individual copper particles have been studied. It has been shown that the main factor determining the activity of the catalysts is the specific surface area of copper. It has been found that the Cu/Al2O3 catalyst containing 60 wt % Cu is the most efficient. A new reaction mechanism is proposed based on the obtained data.

The Pd–Ag/CeO2 catalysts were prepared by the impregnation of highly dispersed CeO2 with a solution of the heteroatomic complex PdAg2(OAc)4(HOAc)4. Samples obtained after the thermolysis of PdAg2(OAc)4(HOAc)4 in N2 and H2 contained Pd–Ag alloy and Pd particles immobilized on CeO2. The Pd0–CeO2 metal oxide centers formed at the interface were highly active in the low-temperature reaction of CO oxidation. The particles of Pd were absent from the Pd–Ag/CeO2 sample prepared by the decomposition of PdAg2(OAc)4(HOAc)4 in an atmosphere of O2; in this case, a significant portion of the Pd–Ag phase was covered with a film of CeO2, which dramatically slowed down the rate of reaction at low temperatures.

The direct conversion of ethanol into the linear primary alcohols C n H2n+1OH (n = 4, 6, and 8) in the presence of the original mono- and bimetallic catalysts Au/Al2O3, Ni/Al2O3, and Au–Ni/Al2O3 was studied. It was established that the rate and selectivity of the reaction performed under the conditions of a supercritical state of ethanol sharply increased in the presence of Au–Ni/Al2O3. The yield of target products on the bimetallic catalyst was higher by a factor of 2–3 than that reached on the monometallic analogs. Differences in the catalytic behaviors of the Au, Ni, and Au–Ni systems were discussed with consideration for their structure peculiarities and reaction mechanisms.