A.J. López-Peinado

Study of oxygen-containing groups in a series of graphite oxides: Physical and chemical characterization

Some graphite oxides with different degrees of oxidation have been prepared by using a modified Staudenmaier method. The oxidation process has been studied by using different techniques: elementary analysis, gas adsorption, X-ray diffraction, FT-IR, XPS and 13C-NMR. The influence of the oxidation degree on the appearance and evolution of new chemical groups in the samples has been analyzed. The oxidation process produces a development of porosity, especially microporosity. FT-IR, XPS and 13C-NMR are complementary techniques, which confirm the existence of hydroxyl, carbonyl, ether, epoxy, and peroxy groups in the more oxidized samples. These surface groups may play an important role in the acid-base bifunctional catalysis.

Oxidation of activated carbon by hydrogen peroxide. Study of surface functional groups by FT-i.r.

Abstract Outgassed activated carbon was oxidized using H2O2 aqueous solutions and the surface oxygen groups were identified by FT-i.r. spectroscopy. The influence of solution concentration and pH, outgassing and oxidation conditions of the carbon, and the addition of catalytic or stabilizer agents to the oxidizing solution was investigated. The stability of the surface groups was also studied for a series of samples. The surface groups initially present in the carbon were largely OH and COC. Oxidation of material with H2O2 solution, at unchanged pH, increased the OH groups present in the oxidized products. With solutions of pH 2.5 and 11.5, the OH groups decreased and various oxygen groups such as CO and C O, or CO2−, were formed. At the lowest pH value, formation of COC structures with an increased number of CO bonds occurred. Ether structures were lost when outgassing under more drastic conditions and when contact with the oxidizing solution was established at very different temperatures. The addition of Fe2+ to the oxidizing solution favoured the oxidation of carbon. However, Fe3+, ethanol and ether were not effective agents. Significant changes in the surface chemistry of samples were observed after a long period of time.

Novel Basic Mesoporous Catalysts for the Friedländer Reaction from 2‐Aminoaryl Ketones: Quinolin‐2(1H)‐ones versus Quinolines

The quinoline ring is present in a number of natural and synthetic products often exhibiting interesting pharmacological activities or physical properties. Different synthetic approaches for the preparation of quinolines have been reported; the Friedl nder reaction (FR) being one of the simplest and most efficient methods. FR is a baseor acid-catalyzed condensation of an aromatic 2-amino-substituted carbonyl compound (aldehyde or ketone) with a carbonyl derivative containing a reactive a-methylene group followed by cyclodehydration (Scheme 1). Generally, the annulation takes place

Study of heat-treated Spanish lignites: characteristics and behaviour in CO2 and O2 gasification reactions

Abstract Six Spanish lignites (raw and demineralized) have been charred to 1113 K in a N 2 atmosphere. The surface area, porosity and mineral matter content of the char coals so obtained have been studied, as well as their reactivity in CO 2 flow in the range 1073–1113 K, and in dry air in the temperature range 733–773 K. The reactivities of the raw chars in CO 2 may be explained according to the different inorganic matter content that may act as catalyst. The demineralization process brings about a lowering in reactivity and an increase, in general, in the apparent activation energy that may be interpreted as being due to a fall in mineral matter content and/or an increase in the amount of feeder pores. With regard to reactivity and apparent activation energy, in the case of dry air three groups of raw chars have been established. The differences between these three groups may be due to the different inorganic impurities present in the raw chars that catalyse the reaction of carbon with O 2 more than the porous texture parameters. Demineralization brings about a lowering in the reactivity values and a levelling off of apparent activation energies. The catalytic effect of iron has also been studied by adding different amounts of this metal to a demineralized char. The burn-off versus time curves of the different char coals have been adjusted by using the τ 0.5 parameter.

Characterization of basic sites of alkaline carbons by Knoevenagel condensation

The characterization of the carbon surface basicity by condensation of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate, diethyl malonate and ethyl bromoacetate as test reactions were studied with a series of lithium, sodium, potassium and cesium exchanged activated carbon (Norit RX 1 Extra). The importance of active sites and the measurement of the surface area in determining the reactivity of the carbons is emphasized. The activity of the carbons increases when the ionic radius of the alkali cation increases; the activity increases in the order Li < Na < K < Cs. Under reaction conditions, it was found that most of the basic sites in alkaline carbons have 10.7 ≤pK a ≤ 13.3 and there are a few sites in the range of 13.3 ≤ pKa ≤ 16.5. The treated activated carbon that had not been subjected to exchange by alkali metal cations exhibited mostly basic sites able to abstract protons with 9 ≤ pKa ≤ 10.7.

Gasification reaction of a lignite char catalysed by Cr, Mn, Fe, Co, Ni, Cu and Zn in dry and wet air

Abstract A Spanish lignite was demineralized and pyrolysed in N 2 atmosphere at 1133 K. On the resulting char, metals from Cr to Zn were deposited from nitrates dissolved in ethanol. The behaviour of these supported catalysts in the reaction with dry and wet air was studied by thermogravimetry in the temperature range 733–773 K. To determine the reactivity per unit catalyst surface site, the dispersion of the metals or metal oxides was measured by X-ray diffraction. The dispersion values found were low; the turnover frequencies (TOF) showed that Cu and Cr (probably in the form of Cr 2 O 3 ) are the best catalysts in this reaction when using either dry or wet air. Apparent activation energies were also obtained in the temperature range used; the Arrhenius plot for the copper-char sample shows that in this case the reaction may be diffusion-limited, although there is considerable increase in reactivity close to Tammanns temperature for copper (678 K). Oxygen chemisorption by Cr 2 O 3 may justify an oxygen transfer mechanism.

The striking behaviour of copper catalysing the gasification reaction of coal chars in dry air

Abstract When copper acts as catalyst in the reaction of oxygen with coal chars, at a certain temperature there is a very high increase in the reactivity value, reaching a region of very low apparent activation energy. This temperature has been identified with that in which the particles of the catalyst wet the surface of the carbon and become mobile. The influences of copper salt and method of preparation of the catalysts, rank of parent coals, residence temperature, time and percentage of Cu and the temperature at which the reactivity is increased have been studied. In some cases this temperature is up to 190 K below the Tammann temperature of CuO (831 K).

Application of basic clays in microwave activated Michael additions: Preparation of N-substituted imidazoles

Abstract Imidazole (C 3 H 4 N 2 ) was condensed with ethyl acrylate (C 5 H 8 O 2 ) using two basic clays (Li + and Cs + montmorillonites) as catalysts in a microwave oven. The catalysts were characterized by chemical analyses, nitrogen adsorption isotherms and X-ray diffraction. Under these experimental conditions N -substituted heterocycles can be obtained with a high activity and selectivity. The role of alkali promoters (Li + and Cs + ) in the montmorillonite for the Michael addition was studied. It was evidenced that the greater the basicity and the irradiation time and power of irradiation were, the higher were the conversion. The yield of the N -substituted imidazole presents a maximum for 0.1 g of Cs-montmorillonite at 850 W in only 5 min of irradiation.

Reactivity of Spanish coal chars in dry air: Effect of the addition of potassium carbonate and acetate

Abstract Several Spanish chars, ranging from lignite to anthracite, were studied in their gasification with dry air. Their behaviour was essentially related to the rank of the parent coal, and mineral matter content. Potassium was added to the demineralized char both as carbonate and acetate. Reactivity of the supported catalysts thus obtained was increased when K 2 CO 3 was the precursor salt. However, this increase was lower, and in some cases there was no increase, when potassium acetate was used. The behaviour found for the two potassium salts, was due to a greater reduction in the surface area of the char when potassium acetate was the precursor salt, which brought about a lower accessibility of the reactant gas to the active surface centres. The effect of K was inhibited in a char because of the high silica content of its ashes.

Alkaline carbons as base catalysts: Alkylation of imidazole with alkyl halides

Abstract Anionic alkylation of imidazole with alkyl halides to produce intermediates in the synthesis of pharmaceutically important antiviral products, such as famciclovir and acyclovir, have been carried out using alkaline carbons as base catalysts. Previously to the alkylation of imidazole, the condensation of benzaldehyde with malonic esters has been used as test reaction of basicity on a series of lithium, sodium, potassium and cesium exchanged Norit RX 1 Extra activated carbon. The importance of active sites and the measurement of surface basicity have been emphasized. Under reaction conditions, it has been found that most of the basic sites in alkaline carbons have 10.7⩽p K a ⩽13.3, but there is a considerable number of sites able to abstract protons of 13.3 ⩽p K a ⩽16.5. Norit RX 1 Extra which was not subject to alkaline exchange retains most of its basic sites capable of abstracting protons of 9 ⩽p K a ⩽10.7. Taking into account that the p K a . of the NH group of imidazole is 14.5, the alkaline carbons present the required basic strength to catalyze the alkylation of this N -heterocycle with alkyl halides.