R. Maggiore

CO2 reforming of methane over Ni–Ru and Ni–Pd bimetallic catalysts

This paper reports the effect of noble metal addition (Ru, Pd) to supported Ni catalysts towards the reaction of CO2 reforming of methane. On the basis of FT-IR spectra of adsorbed CO, H2 chemisorption and TPR measurements it has been proposed that the different behaviour of the Ni-based bimetallic catalysts can be related to different metal–metal interactions occurring on the catalysts. In particular, the strong improvement in the activity and stability observed in the case of ex-nitrate Ni–Ru catalysts has been attributed to an enrichment of the catalyst surface in nickel due to the formation of Ni–Ru clusters with the surface mainly covered by Ni. This leads to an increase in the metallic dispersion of Ni and favours the formation of more reactive intermediate carbonaceous species.

Influence of the support on CO2 methanation over Ru catalysts : An FT-IR study

The hydrogenation of CO2 to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO2. Ru/ZSM-5 was more selective to methane than Ru/SiO2. On the basis of FT-IR spectra of CO and CO2 adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane.

Hydrogen spillover effects in the hydrogenation of benzene over Ptγ-Al2O3 catalysts

A study has been made of the presence of hydrogen spillover on Ptγ-Al2O3 catalysts and its influence on the hydrogenation of benzene to cyclohexane. The specific activity, referred to Pt metal, increases with the degree of dilution of the catalyst with the γ-Al2O3 support up to 501 and remains almost constant in more diluted systems; this indicates that atomic hydrogen does not migrate beyond a certain distance, depending on the granulation and texture of the solid mixture. The results suggest that hydrogenation occurs both on the Ptγ-Al2O3 and on the diluentγ-Al2O3. The ratio between the specific conversion of diluted and undiluted catalysts is temperature independent and the Arrhenius plots for various (un)diluted catalysts all show an equal apparent activation energy value of 9.16 kcal/mol. A hypothesis for the hydrogenation mechanism of benzene over the γ-Al2O3 diluent is reported.

FT-IR characterization of alkali-doped Pd catalysts for the selective hydrogenation of phenol to cyclohexanone

A detailed FT-IR investigation of CO, phenol and cyclohexanone adsorbed on alkali-doped Pd catalysts has been carried out in order to get information on the influence of the support and of the addition of promoters (alkali or alkaline earth metals) on the catalytic performance of Pd-supported catalysts in the selective hydrogenation of phenol. The obtained results are consistent with a mechanism that involves the reaction of phenol, adsorbed on the support as a phenolate species, located nearby Pd sites on which hydrogen is activated. The basicity of the support plays an important role in the adsorption of the phenol. Promoters have been found to modify the electronic properties of the palladium sites.

Activated carbons : In vitro affinity for fumonisin B1 and relation of adsorption ability to physicochemical parameters

In vitro affinity tests were conducted to assess the effectiveness of 19 activated carbons (ACs), hydrated sodium calcium aluminosilicate (HSCAS), and sepiolite (S) in binding fumonisin B1 (FB1) from solution. Relationships between adsorption ability and physicochemical parameters of ACs (specific surface area, iodine value, and methylene blue index) were tested. When 5 ml of a 4-μg/ml aqueous solution of FB1 was treated with 10 mg of AC, ACs adsorbed 0.46 to 100% of the FB1. HSCAS and S were not effective in binding FB1. In two saturation tests carried out with decreased amounts of sorbent (5 and 2 mg, respectively), three ACs also showed high adsorption ability (adsorbing 96.48 to 99.20% of the FB1) A general relationship between adsorption ability and the physicochemical parameters of the ACs was observed, supporting the inference of a close relationship between molecule trapping and surface physicochemical adsorption processes. The methylene blue index was more reliable than iodine number and surface area for predicting ability of ACs to adsorb FB1. In tests of simultaneous adsorption ability carried out using 5 ml of a solution containing 10 μg/ml FB1 plus 50 μg/ml aflatoxin B1 (AFB1)and 2 or 5 mg of sorbent, ACs showed a higher affinity for AFB1 than for FB1. However, two ACs bound ca. 100% of the two mycotoxins. When 5 ml of an aqueous extract solution obtained from naturally contaminated corn containing 1.84 μg/ml FB1 and 0.042 μg/ml AFB1 was treated with 10 mg of sorbent, one AC adsorbed ca. 95% and 99% of FB1 and AFB1, respectively. It is concluded that certain ACs have high in vitro affinity for FB1 and AFB1 singly or in combination, and may hold promise as multi-mycotoxin sequestering agents. However, further in vivo investigations are neededto confirm the abilities of ACs to sequester the most important mycotoxins singly or in combinations, establish the amounts to be added to feeds, and determine any long-term effects they may have on gastrointestinal absorption of essential nutrients.

Effect of the acid–base properties of Pd–Ca/Al2O3 catalysts on the selective hydrogenation of phenol to cyclohexanone: FT-IR and TPD characterization

Abstract The effect of the addition of calcium as promoter on the acid–base properties of the Pd/Al 2 O 3 system has been studied by FT-IR of pyridine, pyrrole and CO 2 adsorbed and by TPD of CO 2 in order to better clarify the role of calcium on the performance of palladium supported catalysts in the selective hydrogenation of phenol to cyclohexanone. The obtained results have shown that the addition of calcium causes a decrease in the acidity of the system, essentially in terms of amount of acid sites, and a corresponding increase in the number and strength of the basic sites. It has been suggested that the promoter enhances the catalytic performance of Pd/Al 2 O 3 through a variation of the acid–base characteristics of the support leading to a modification of the electronic surroundings of Pd sites on which hydrogen is activated.

Temperature-programmed reduction. Metal-support interaction on supported monometallic Ru and Cu Catalysts

Ru and Cu samples supported on SiO2, Al2O3 and MgO were studied by the temperature-programmed reduction (TPR) technique. Experiments were carried out both on unreduced impregnated salts and after oxidation of already reduced samples.The TPR profiles were found to be strongly dependent on the support used, indicating different degrees of interaction between the metal and the support, which can be ranked as MgO≫Al2O3>SiO2. It is suggested that the interaction occurs through the formation of surface complexes difficult to reduce. The decrease in hydrogen consumption observed on the Ru samples with the number of TPR cycles is attributed to the difficulty in oxidizing large Ru particles.ZusammenfassungAuf SiO2, Al2O3 und MgO aufgebrachte Ru- und Cu-Proben wurden mittels temperaturprogrammierter Reduktion (TPR) untersucht. Experimente wurden sowohl an unreduzierten Salzimprägnierungen als auch nach Oxydation von bereits reduzierten Proben ausgeführt. Die TPR-Profile sind stark vom benutzten Trägen abhängig, was auf unterschiedliche Grade der Wechselwirkung zwischen Metall und Träger hindeutet; die Reihenfolge ist MgO≫Al2O3>SiO2. Es wird vermutet, daß das Wesen der Wechselwirkung in der Bildung von schwer reduzierbaren Oberflächenkomplexen zu suchen ist. Die bei Ru-Proben mit der Zahl der TPR-Zyklen beobachtete Verminderung des Wasserstoffverbrauchs wird mit der Schwierigkeit, große Ru-Partikel zu oxydieren, in Zusammenhang gebracht.РезюмеМетодом температурн о-программируемого восстановления (ТПВ) и зучены образцы меда и рутения на подл ожках из SiO2, Аl2О3 и MgO. Эксперимента были пр оведены как с невосстановленными импрегнированными о бразцами, так и с окисленными, но пре дварительно подвергнутих восста новлению, образцами. Н айдено, что профили ТПВ сильно за висят от используемой подлож ки, показывая тем самы м различные степени взаимодейст вия между металлом и подложкой в следующей последов ательности MgO≫ Al2O3>SiO2. Предположено, что такие взаимодейс твия протекают с обра зованием на поверхности комплек сов, трудно подвергающихся восс тановлению. Наблюдае мое в случае образцов рутения уме ньшение расхода водорода от ч исла циклов ТПВ, объяс нено трудностью окислени я больших частиц рутения.

Performance of supported Ru-Cu bimetallic catalysts prepared from nitrate precursors

Bimetallic Ru-Cu catalysts supported on SiO2, α-Al2O3, γ-Al2O3 have been prepared using precursors which do not contain chlorine and characterized by CO chemisorption and TPR. Catalytic activity has been tested in the propane hydrogenolysis. It has been observed that the degree of formation of bimetallic Ru-Cu aggregates depends on the support used. It is suggested that the degree of interaction between Ru and Cu is strongly influenced by the strength of the metal-support interaction.

Bimetallic RuCu/SiO2 catalysts: Effect of total surface area on the catalytic properties

Abstract Bimetallic RuCu samples supported on silica gel having different surface areas have been characterized by TPR (temperature programmed reduction) and CO chemisorption. The catalytic properties have been tested in the hydrogenolysis of propane. Ruthenium and copper salts which do not contain chlorine have been used for catalyst preparation. The surface area of the supports used ranged from 25 to 500 m 2 /g. The Cu/Ru atomic ratio was varied between 0 and 4. Addition of Cu decreases the catalytic activity and increases the selectivity to ethane. The largest variations are observed on the support with larger surface area. It is suggested that a larger RuCu interaction occurs on the smaller metal particles due to the higher tendency of the Cu atoms of populating low coordination sites.

RuCuZSM5 catalysts: characterization by FT-IR spectroscopy

Abstract H-ZSM5 supported RuCu bimetallic catalysts have been studied by FT-IR spectroscopy. Experiments have been carried out on samples prepared from Ru(NO)(NO3)3 and RuCl3. On the monometallic Ru ZS M 5 samples adsorption of CO led to a band at 2046 cm−1, due to CO linearly adsorbed on Ru0, and several bands at higher frequencies related to CO on Ruδ+ species. A higher amount of Ruδ+ species is formed on the ex-Ru(NO)(NO3)3 sample, due to the smaller metal particle size of this sample compared to the ex-RuCl3 one. On monometallic Cu ZSM 5 two bands at 2151 and 2158 cm−1 are observed, both related to CO adsorbed on Cu+1 sites, formed through a reaction with the OH groups of the zeolite. On the bimetallic RuCu samples, besides all the characteristic bands of the Ru and Cu monometallic samples, a band at 2138 cm−1, attributed to CO adsorbed on Cu bound to Ru has been detected, denoting the formation of RuCu bimetallic particles. The FT-IR spectra indicate that on the samples prepared from RuCl3 the extent of bimetallic RuCu particles is higher than on those prepared from Ru(NO)(NO3)3. This behaviour, attributed to the presence of chlorine on the ex-RuCl3 samples, is in agreement with the catalytic performance of these systems in the hydrogenolysis of propane.