Selective hydrogenation of maleic anhydride to γ-butyrolactone and tetrahydrofuran by Cu–Zn–Zr catalyst in the presence of ethanol

A series of Cu–Zn–Zr catalysts were prepared by a coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N₂ adsorption. The catalytic activity of the Cu–Zn–Zr catalyst in the hydrogenation of maleic anhydride using ethanol as a solvent was studied at 220–280 °C and 1 MPa. Maleic anhydride was mainly hydrogenated to γ-butyrolactone and tetrahydrofuran while ethanol dehydrogenated to ethyl acetate. After reduction, CuO species present in the calcined Cu–Zn–Zr catalysts were converted to metallic copper (Cu⁰). The presence of ZrO₂ favored the deep hydrogenation of γ-butyrolactone to tetrahydrofuran while the presence of ZnO was beneficial to the formation of the intermediate product γ-butyrolactone. The molar ratios of the hydrogen produced in ethanol dehydrogenation to the hydrogen consumed in maleic anhydride hydrogenation increased with the increase of the reaction temperature.     

Development of new catalytic systems for upgraded bio-fuels production from bio-crude-oil and biodiesel

The investigation of upgraded bio-fuels production processes was carried out via the development of efficient catalysts for oxy-organic hydrodeoxygenation (HDO) processes. It was found that Ni–Cu catalysts are more attractive than single Ni catalysts in HDO under mild conditions. Copper facilitates the nickel oxide reduction at temperatures lower than 300 °C. Moreover, copper prevents methanization of oxy-organics at 280–350 °C. The catalyst supports play also a key role in hydrotreatment of oxygen-containing compounds. Screening of catalyst supports showed that CeO₂ and ZrO₂ are most effective in the target processes because of possible additional activation of oxy-compounds on the support surface. The prepared catalysts have non-sulfided nature and can be used for upgrading of bioliquids with a low sulfur content.     

Selective steam reforming of methanol over silica-supported copper catalyst prepared by sol–gel method

Silica-supported copper prepared by a sol–gel method can selectively catalyze methanol steam reforming to hydrogen and carbon dioxide at 250 °C. The catalytic activity increases with the copper content up to 40 wt.%. The selectivity to carbon monoxide with the catalysts containing 20–40 wt.% of copper is significantly lower than that with a commercial Cu/ZnO/Al₂O₃ catalyst. Copper particles are highly dispersed in the catalyst whose Cu content is 20 wt.% or less. After the reaction at 250 °C the particles are present as Cu₂O with the mean crystallite size less than 4 nm. In the catalyst with the Cu content of 30–50 wt.%, the fine Cu₂O particles coexist with large metallic Cu particles whose mean crystallite size is 30–40 nm after the reaction. The large metallic particles are supposed to contribute to the reaction as well as the fine Cu₂O particles although the surface area is estimated to be significantly smaller than that of the latter.     

Hydrogenation of quinoline by ruthenium nanoparticles immobilized on poly(4-vinylpyridine)

A series of catalysts composed of ruthenium nanoparticles immobilized on poly(4-vinylpyridine) was prepared by NaBH₄ reduction of RuCl₃ · 3H₂O in methanol in the presence of the polymer; TEM measurements of a 10 wt% Ru/P4VPy material indicate that ruthenium particles of 1–2 nm predominate. This catalyst is efficient for the selective hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline at 100–120 °C and 30–40 bar H₂. The activity increases with hydrogen pressure up to 40 bar but is essentially independent of quinoline concentration. Polar solvents, triethylamine, and acetic acid enhance catalytic performance, suggesting an ionic mechanism involving heterolytic hydrogen activation.     

The catalytic activity of CuO–CeO2 mixed oxides for diesel soot oxidation with a NO/O2 mixture

Copper doped ceria and ceria–zirconia mixed oxides were synthesized using the citric acid sol–gel method. The temperature-programmed oxidation (TPO) results showed that the Cu modification improved the low-temperature activity and the selectivity to CO₂ of ceria for soot oxidation in the presence of NO and excess oxygen even after ageing at 800 °C for 20 h in flow air. Meanwhile, not only the segregation of Cu and sintering of CuO, but also the separation of Ce- and Zr-rich phases worsened the activity of the Cu–Ce–Zr catalyst after the high-temperature calcination.     

Photophysical and photocatalytic properties of nanosized copper-doped titania sol–gel catalysts

The effect of doping the TiO₂ lattice with copper was studied. TiO₂–Cu semiconductors (0.1, 0.5, 1.0 and 5.0 Cu wt.%) were synthesized by the sol–gel method by incorporating Cu (NO₃)₂ into the titanium alkoxide solution. In the samples thermally treated at 500 °C, mesoporous materials (9.5–12 nm) with specific surface areas of 90–52 m²/g were obtained. The X-ray diffraction (XRD) patterns of the annealed samples present anatase as the sole nanocrystalline phase (28 nm). The UV–vis diffuse reflectance spectra of the Cu-doped samples show a shift in the band gap to lower energy levels. The X-ray photoelectron spectroscopy (XPS) reveals a reduction in the oxidation state of the copper precursor, Cu(II), stabilizing Cu(0) and Cu(I) in the annealed solids. The photocatalytic test for the 2,4-dichlorophenoxyacetic acid degradation showed high efficiency and mineralization up to 92% (total organic carbon, TOC) in the Cu-doped sol–gel materials. The enhancement of the photocatalytic activity was discussed as an effect due to the Cu content as well as to the formation of stable Cu(I) in the Cu-doped TiO₂ semiconductors.     

Preparation, characterization and catalytic properties of carbon nanofiber-supported Pt, Pd, Ru monometallic particles in aqueous-phase reactions

Carbon nanofibers (CNF) synthesized by catalytic chemical vapor deposition (CVD) method were used to prepare supported platinum, palladium and ruthenium monometallic (2.0 wt.%) catalysts by means of incipient-wetness impregnation method. The CNF support and catalysts were characterized by X-ray powder diffraction (XRD), nitrogen adsorption/desorption isotherms, volumetric chemisorption of hydrogen, temperature-programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). Solids were tested in catalytic wet-air oxidation (CWAO) of phenol aqueous solution (180–240 °C and 10.0 bar of oxygen partial pressure) carried out in a continuous-flow trickle-bed reactor. Trends of phenol and total organic carbon (TOC) conversion demonstrate that the CNF support and CNF-Pt catalyst did not exhibit constant activity for CWAO of phenol. A decrease of catalyst activity, detection of carbon dioxide in the off-gas stream while examining catalyst stability and significant textural changes observed, provide an evidence that under net oxidizing reaction conditions gasification of the CNF support occurs. The prepared catalysts were also tested in liquid-phase thermal decarboxylation of formic acid in inert atmosphere (60–220 °C). Among solids examined, the CNF-Pd exhibited the highest activity. At the employed conditions, no decomposition of the CNF support was observed during the thermal decarboxylation of formic acid.     

Gas phase hydrogenation of maleic anhydride to tetrahydrofuran by Cu/ZnO/TiO2 catalysts in the presence of n-butanol

Cu/ZnO/TiO₂ catalysts were prepared via the coprecipitation method. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectrometry, temperature programmed reduction, and N₂ adsorption. The catalytic activity of Cu/ZnO/TiO₂ catalyst in gas phase hydrogenation of maleic anhydride in the presence of n-butanol was studied at 235–280 °C and 1 MPa. The conversion of maleic anhydride was more than 95.7% and the selectivity of tetrahydrofuran was up to 92.7%. At the same time, n-butanol was converted to butyraldehyde and butyl butyrate via reactions, namely, dehydrogenation, disproportionation, and esterification. There were two kinds of CuO species present in the calcined Cu/ZnO/TiO₂ catalysts. At a lower copper content, the CuO species strongly interacted with ZnO and TiO₂; at a higher copper content, both the surface-anchored and bulk CuO species were present. The metallic copper (CuO) produced by the reduction of the surface-anchored CuO species favored the deep hydrogenation of maleic anhydride to tetrahydrofuran. The deep hydrogenation activity of Cu/ZnO/TiO₂ catalyst increased with the decrease of crystallite sizes of CuO and the increase of microstrain values. Compensations of reaction heat and H₂ in the coupling reaction of maleic anhydride hydrogenation and n-butanol dehydrogenation were distinct.     

Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

Catalytic hydrogen production from dimethyl ether over CuFe2O4 spinel-based composites: Hydrogen reduction and metal dopant effects

Investigation of hydrogen reduction pretreatment and metal doping to Cu–Fe spinel catalyst coupled with γ-alumina was performed in dimethyl ether steam reforming for hydrogen production. The high activity and stability of the catalysts were achieved when the catalysts were reduced at or below 350 °C due to the stability of obtained Cu and Fe₃O₄ phases. Reduction at higher temperatures of 450 and 600 °C would bring about the decrease in activity and stability because the resultant Fe₃O₄ was further reduced to metallic Fe, and sintering of metallic Cu and Fe proceeded. Dopants (Mn, Cr, Co, and Al) could affect the reforming performance in terms of both activity and selectivity to products.     

On the role of the thermal treatment of sulfided Rh/CNT catalysts applied in the oxygen reduction reaction

Low loading sulfided rhodium catalysts supported on carbon nanotubes (CNTs) were prepared from RhCl₃ by deposition–precipitation using hydrogen peroxide, followed by an exposure to hydrogen sulfide and an additional thermal treatment in the range from 400 °C to 900 °C. Hydrogen sulfide was generated online from hydrogen and sulfur vapor over molybdenum disulfide as catalyst. By elemental analysis, the Rh loading of the prepared catalysts was found to be 1.4–1.8 wt%. Morphology and composition of the resulting catalysts were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and X-ray photoelectron spectroscopy (XPS). Nanoparticles were found to be highly dispersed on the CNTs with an average diameter as small as 1.0 nm determined by TEM. Sintering occurred during heat treatments at 650 °C and 900 °C in helium, as evidenced by XRD, TEM, and XPS. The treatment with hydrogen sulfide significantly enhanced the activity of the supported rhodium catalysts for the oxygen reduction reaction (ORR) in hydrochloric acid, as determined by rotating disc electrode measurements. The sulfided catalyst annealed at 650 °C with a particle size of about 2.5 ± 1.0 nm showed the best performance for the ORR, which is discussed based on the presence of a more stable rhodium sulfide layer on the metallic rhodium particles.     

Co–Ni Catalysts Derived from Hydrotalcite-Like Materials for Hydrogen Production by Ethanol Steam Reforming

A series of Co–Ni catalysts, prepared from hydrotalcite (HT)-like materials by co-precipitation, has been studied for the hydrogen production by ethanol steam reforming. The total metal loading was fixed at 40% and the Co–Ni composition was varied (40–0, 30–10, 20–20, 10–30 and 0–40). The catalysts were characterized using X-ray diffraction, N₂ physisorption, H₂ chemisorption, temperature-programmed reduction, scanning transmission electron microscope and energy dispersive spectroscopy. The results demonstrated that the particle size and reducibility of the Co–Ni catalysts are influenced by the degree of formation of a HT-like structure, increasing with Co content. All the catalysts were active and stable at 575 °C during the course of ethanol steam reforming with a molar ratio of H₂O:ethanol = 3:1. The activity decreased in the order 30Co–10Ni > 40Co ~ 20Ni–20Co ~ 10Co–30Ni > 40Ni. The 40Ni catalyst displayed the strongest resistance to deactivation, while all the Co-containing catalysts exhibited much higher activity than the 40Ni catalyst. The hydrogen selectivities were high and similar among the catalysts, the highest yield of hydrogen was found over the 30Co–10Ni catalyst. In general, the best catalytic performance is obtained with the 30Co–10Ni catalyst, in which Co and Ni are intimately mixed and dispersed in the HT-derived support, as indicated by the STEM micrograph and complementary mapping of Co, Ni, Al, Mg and O.     

Highly active and selective Cu/SiO2 catalysts prepared by the urea hydrolysis method in dimethyl oxalate hydrogenation

Cu/SiO₂ catalysts have been successfully prepared via urea hydrolysis method. The catalysts have been systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, N₂-physisorption and H₂ temperature-programmed reduction. The results demonstrated the presence of copper nanoparticles and their high dispersion on the SiO₂ support. Catalysts with different copper loadings were prepared, and their performances in the hydrogenation of dimethyl oxalate to ethylene glycol were studied. A 100% conversion of dimethyl oxalate and maximum 98% selectivity of ethylene glycol were reached with 15.6 wt.% copper loading at 200 °C and 2 MPa. Furthermore, under the same reaction conditions, the catalyst can maintain the selectivity of 90% when the reduction temperature reduced from 350 °C to 200 °C. The high activity and selectivity over the catalyst may be ascribed to the homogenously distribution of copper nanoparticles on the large surface.     

Selective oxidation of ethane: Developing an orthorhombic phase in Mo–V–X (X = Nb, Sb, Te) mixed oxides

Mo–V–X (X = Nb, Sb and/or Te) mixed oxides have been prepared by hydrothermal synthesis and heat-treated in N₂ at 450 °C or 600 °C for 2 h. The calcination temperature and the presence or absence of Nb determines the nature of crystalline phases in the catalyst. Nb-containing catalysts heat-treated at 450 °C are mostly amorphous solids, while Nb-free catalysts heat-treated at 450 °C and samples treated at 600 °C clearly contain crystalline phases. TPR-H₂ experiments show higher H₂-consumption on catalysts with amorphous phases. Catalytic results in the oxidative dehydrogenation of ethane indicate that the selective production of the olefin is strongly related to the development of the orthorhombic Te₂M₂₀O₅₇ or (SbO)₂M₂₀O₅₆ (M = Mo, V, Nb) phase (the so-called M1 phase), which is mainly formed at 600 °C. This active and selective crystalline phase is characterized to show moderate reducibility and active centers enough for the selective oxidative activation of ethane with the minimum quantity possible of active centers for ethylene activation. In this sense, the best yield to ethylene has been achieved on a Mo–V–Te–Nb mixed oxide.     

Platinum-based Alloys as oxygen–reduction Catalysts for Solid–Polymer–Electrolyte Direct Methanol Fuel Cells

Electrocatalytic activities of various carbon-supported platinum-based binary, namely, Pt–Co/C, Pt–Cr/C and Pt–Ni/C, and ternary, namely, Pt–Co–Cr/C and Pt–Co–Ni/C, alloy catalysts towards oxygen reduction in solid–polymer–electrolyte direct methanol fuel cells were investigated at 70°C and 90°C both at ambient and 2bar oxygen pressures. It was found that Pt–Co/C exhibits superior activity relative to Pt/C and other alloy catalysts.     

Non-oxidative dehydrogenation of ethane to ethylene over chromium catalysts prepared from layered double hydroxide precursors

Non-oxidative dehydrogenation of ethane into ethylene at 700 °C over reductively pretreated Cr–Mg–Al and Cr–Mg mixed oxide catalysts has been studied. The catalysts were prepared from layered double hydroxide (LDH) precursors that contained various species of chromium (i.e., cationic Cr(III), complex of Cr(III) with an anionic chelating agent, and chromate anion). Synthesized materials were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy techniques. It was shown that the surface area of the LDH-derived mixed oxides, their catalytic performance, coking ability, and susceptibility to sintering were highly dependent on the method used for introducing chromium into the LDH precursors of the catalysts.     

Combinatorial approach to the preparation and characterization of catalysts for biomass steam reforming into syngas

A number of catalysts based on Al₂O₃ loaded with doped Ce-Zr mixed oxides and different active components (Cu, Cu-Ni, Ru, Pt, etc.) were synthesized via standard wet impregnation method using the robotic workstation. Ethanol (EtOH) was taken as a model compound of bio-oil and steam reforming of ethanol (ESR)—as a model reaction. Activity screening experiments performed at 600–700 °C in 0.5 vol.% C₂H₅OH + 2.5 vol.% H₂O + 97 vol.% He mixture revealed that the most effective catalyst composition is Ru/Ce_0.4Zr_0.4Sm_0.2/Al₂O₃. Catalytic activity investigations at high reagent concentrations (10 vol.% C₂H₅OH + 40 vol.% H₂O + 50 vol.% N₂) at 650–800 °C confirmed this fact, revealing also that at high temperatures the activity of Cu-Ni catalysts is comparable with that of Ru-containing catalyst.     

Gold supported on mesoporous titania thin films for application in microstructured reactors in low-temperature water-gas shift reaction

Au (1 wt.%)/TiO₂ catalytic thin films were prepared on a surface-modified titanium substrate for application in a water-gas shift (WGS) microstructured reactor. Au-containing mesoporous titania films were synthesized using Pluronic 127 surfactant as a structure directing agent and titanium tetrabutoxide as titania source. Colloidal gold nanoparticles of 4 nm diameter were added to the synthesis sol prior to spin-coating. The resulting thin films were characterized by X-ray diffraction, transmission electron microscopy, ethanol adsorption–desorption isotherms and spectroscopic ellipsometry. Catalytic activity and selectivity were measured for the WGS reaction at temperatures between 220 and 290 °C. The reaction rate measured at CO conversions of below 10% was similar to that reported for gold supported on mesoporous titania and on ceria modified mesoporous titania pelletized catalysts prepared via deposition–precipitation.     

Cu/Al2O3 catalysts for soot oxidation: Copper loading effect

Cu/Al₂O₃ catalysts with metal loading from 0.64 to 8.8 wt.% have been prepared and characterized by different techniques: N₂ adsorption at −196 °C (BET surface area), ICP (Cu loading), XRD, selective copper surface oxidation with N₂O (Cu dispersion), TPR-H₂ (redox properties), and XPS (copper surface species). The catalytic activity for soot oxidation has been tested both in air and NO_x/O₂. The activity in air depends on the amount of easily-reduced Cu(II) species, which are reduced around 275 °C under TPR-H₂ conditions. The amount of the most active Cu(II) species increases with the copper loading from Cu_1% to Cu_5% and remains almost constant for higher copper loading. In the presence of NO_x, the first step of the mechanism is NO oxidation to NO₂, and the catalytic activity for this reaction depends on the copper loading. For catalysts with copper loading between Cu_1% and Cu_5%, the catalytic activity for soot oxidation in the presence of NO_x depends on NO₂ formation. For catalysts with higher copper loading this trend is not followed because of the low reactivity of model soot at the temperature of maximum NO₂ production. Regardless the copper loading, all the catalysts improve the selectivity towards CO₂ formation as soot oxidation product both under air and NO_x/O₂.     

Dynamic in situ observation of automotive catalysts for emission control using X-ray absorption fine structure

Two main pivotal subjects of research in automotive catalysts were studied by modern X-ray absorption analysis techniques. One is oxygen storage/release behaviour, and the other is sintering inhibition of Pt particles. First, three types of CeO₂–ZrO₂ (Ce:Zr = 1:1 molar ratio) compounds with different oxygen storage/release capacities and different structural properties were prepared, and the valence change of Ce as a function of temperature during oxygen release/storage processes was investigated. The reduction of surface Ce mainly occurred in the range 100–170 °C, and the reduction of bulk Ce progressed at high temperatures of 170 °C and above. The Ce reduction behaviour depended not only on the homogeneity of the Ce and Zr for bulk reduction at high temperatures but also on the particle size of the CeO₂–ZrO₂ samples for surface reduction at low temperatures. Secondly, sintering inhibition of Pt in Pt/Al₂O₃, Pt/MgO and Pt/ceria-based catalysts after 800 °C ageing in air was studied. We found that the Pt–O–M (M = Mg, Ce) bond acted as an anchor and inhibited the sintering of Pt particles on MgO or ceria-based oxide. Especially, it was noteworthy that the Pt–O–Ce⁴⁺ bond on the ceria-based support breaks easily through the reduction of Ce (Ce⁴⁺ → Ce³⁺) during the usual stoichiometric and reducing conditions.