Leonardus Lefferts

Development of monolith with a carbon-nanofiber-washcoat as a structured catalyst support in liquid phase

Washcoats with improved mass transfer properties are necessary to circumvent concentration gradients in case of fast reactions in liquid phase, e.g. nitrate hydrogenation. A highly porous, high surface area (180 m2/g) and thin washcoat of carbon fibers, was produced on a monolith support by methane decomposition over small nickel particles. Carbon fibers form a homogeneous layer less then 1 ?m thin, covering the surface of the channels in the monolith. The fibers penetrated into the cordierite, which is suggested to cause a remarkable stability of the fibers against ultrasound maltreatment. The texture of the fibers is independent of both the thickness of the ?-alumina washcoat as well as the time to grow carbon fibers.

Oxidative conversion of propane over lithium-promoted magnesia catalyst. I. Kinetics and mechanism

Oxidative conversion of lower alkanes over lithium-promoted magnesia catalysts offers a viable alternative for propene and ethene production. The catalytic performance of propane oxidative dehydrogenation and cracking shows yields up to 50% of olefin (propene and ethene). The reaction kinetics were studied by means of variation of the partial pressures of the reactants as well as by addition of product species to the reaction mixture. The observations can be qualitatively explained with a mechanism including activation of propane on the catalyst generating propyl radicals that undergo a radical-chain mechanism in the gas phase. Alkane activation is rate determining. Oxygen has two functions in the mechanism. First, the presence of small amounts of oxygen influences the radical gas-phase chemistry significantly because the type and concentration of chain propagator radicals are greatly increased. At higher oxygen partial pressures the radical chemistry is only slightly influenced by the increasing oxygen concentration. The second function of oxygen is to facilitate the removal of hydrogen from the surface OH? species that are formed during the activation of propane on the catalyst. Carbon dioxide has a strong inhibiting effect on the reaction without changing the product distribution, due to strong adsorption on the site that activates propane.

In situ catalytic pyrolysis of lignocellulose using alkali-modified amorphous silica alumina

Canadian pinewood was pyrolyzed at 450 °C in an Infrared oven and the pyrolysis vapors were converted by passing through a catalyst bed at 450 °C. The catalysts studied were amorphous silica alumina (ASA) containing alkali metal or alkaline earth metal species including Na, K, Cs, Mg and Ca. The catalysts effectiveness to reduce the bio-oil oxygen content, to enhance the bio-oil energy density and to change the liquid and gas product distribution were evaluated using different techniques including gravimetric analysis, elemental analysis, Karl-Fischer titration, GC/MS and micro-GC analysis. According to the results K/ASA found to be the most effective catalysts for conversion of hollocellulose (hemicellulose and cellulose)-derived vapors of pinewood while Cs/ASA catalyst was the most effective catalyst for conversion of lignin-derived vapors and production of hydrocarbons.

The oxidative dehydrogenation of methanol to formaldehyde over silver catalysts in relation to the oxygen-silver interaction

The properties of silver in the oxidative dehydrogenation of methanol were studied in a flow reactor under near industrial conditions. The influences of temperature, concentration of both reactants, gas velocity, space velocity, the form of the silver catalyst and surface composition of the catalyst were studied. A model for the reaction is proposed which is based on the experimental observations and on the nature of the interaction of silver with oxygen. It issuggested that different oxygen species on the silver surface play different roles in the reactions to CO, CO2 and H2CO. Gas phase reactions only contribute to the conversion to CO.

Conversion of lignocellulosic biomass to green fuel oil over sodium based catalysts

Upgrading of biomass pyrolysis vapors over 20 wt.% Na2CO3/γ-Al2O3 catalyst was studied in a lab-scale fix-bed reactor at 500°C. Characterization of the catalyst using SEM and XRD has shown that sodium carbonate is well-dispersed on the support γ-Al2O3. TGA and (23)Na MAS NMR suggested the formation of new hydrated sodium phase, which is likely responsible for the high activity of the catalyst. Catalytic oil has much lower oxygen content (12.3 wt.%) compared to non-catalytic oil (42.1 wt.%). This comes together with a tremendous increase in the energy density (37 compared to 19 MJ kg(-1)). Decarboxylation of carboxylic acids was favoured on the catalyst, resulting to an oil almost neutral (TAN=3.8mg KOH/g oil and pH=6.5). However, the mentioned decarboxylation resulted in the formation of carbonyls, which correlates to low stability of the oil. Catalytic pyrolysis results in a bio-oil which resembles a fossil fuel oil in its properties.

Oxidative conversion of propane over lithium-promoted magnesia catalyst. II. Active site characterization and hydrocarbon activation

Activation of propane over Li/MgO catalyst has been investigated. It is shown that a small fraction of the oxygen ions in Li/MgO catalysts can be removed from the catalyst by reduction treatment in H2 at 600 °C. Catalytic activity of Li/MgO exhibits a strong correlation to the amount of oxygen that is removed. It is proposed that the sites containing removable oxygen are responsible for the activation of propane. About 70 propane molecules were converted after consumption of one such oxygen site, in the absence of gas-phase oxygen, implying a mechanism in which propane molecules are activated on the catalyst resulting in propyl radicals that are released to the gas phase where they undergo chain propagation reactions, resulting in the products observed. The active O site is consumed by conversion into an OH group, as the oxygen is not removed from the catalyst with propane. The oxidative conversion of propane over Li/MgO catalysts follows a mixed heterogeneous-homogeneous radical chemistry where the catalyst acts as an initiator. At low propane partial pressures (0.1 bar), the catalyst surface area to volume ratio of the catalytic reactor does not influence the chain length in the propagation step. At higher propane partial pressures (>0.3 bar), favoring extensive gas-phase reactions, the catalyst affects conversion and selectivity also via quenching and chain termination.

Humin based by-products from biomass processing as a potential carbonaceous source for synthesis gas production

Lignocellulosic biomass is addressed as potential sustainable feedstock for green fuels and chemicals. (Hemi)cellulose is the largest constituent of the material. Conversion of these polysaccharides to bio-based platform chemicals is important in green chemical/fuel production and biorefinery. Hydroxymethyl furfural, furfural and levulinic acid are substantial building blocks from (poly)saccharides. Synthesis of these molecules involves acid catalysed hydrolysis/dehydration reactions which leads large formation of insoluble by-products, called humins. Humin obtained from dehydration of glucose is used in this study. Fractionisation of humin was investigated using various solvents (e.g., acetone, H2O, and NaOH 1%). Characterisation of humin using various techniques including ATR-IR, HR-SEM, solid state NMR, elemental analysis, Raman spectroscopy, pyrolysis, etc. confirms its furan rich structure with aliphatic oxygenate linkages. The influence of thermal treatment on humin was investigated. Humin undergoes a lot of changes both in morphology and structure. Humin loses ca. 45 wt% when preheated to 700 °C (prior to the gasification temperature) and contains above 92 wt% C in mainly aromatic/graphitic structures. Valorisation of humin via dry reforming was studied. Non-catalytic dry reforming of humin is very difficult; however, alkali catalysts (e.g. Na2CO3) can enhance the reaction rate tremendously.

Valorization of Humin‐Based Byproducts from Biomass Processing—A Route to Sustainable Hydrogen

The synthesis of biomass-based top value-added chemical platforms, for example, 5-hydroxymethyl furfural, furfural, or levulinic acid from the acid-catalyzed dehydration of sugars results in high yields of insoluble by-products, referred to as humin. Valorization of humin by steam reforming for H2 is discussed. Both thermal and catalytic steam gasification were investigated systematically. Humin undergoes drastic changes under thermal pre-treatment to the gasification temperature. Alkali-metal-based catalysts were screened for the reactions. Na2 CO3 showed the highest activity and was selected for further study. The presence of Na2 CO3 enhances the gasification rate drastically, and gas-product analysis shows that the selectivity to CO and CO2 is 75% and 25%, respectively, which is a H2 /CO ratio of 2 (corresponding to 81.3% H2 as compared to the thermodynamic equilibrium). A possible process for the complete, efficient conversion of humin is outlined.

Ceria Nanocatalysts: Shape Dependent Reactivity and Formation of OH

Ceria nanoshapes (octahedra, wires, and cubes) were investigated for CO adsorption and subsequent reaction with water. Surprisingly, the reactivity of specific OH groups was explicitly determined by the ceria nanoshape. The nanoshapes showed different levels of carbonates and formates after exposure to CO, the amount of carbonates increasing from octahedral≪wires

The importance of acid site locations for n-butene skeletal isomerization on ferrierite

The role of the previous termacid site locationnext term in H-ferrierite (H-FER) on the skeletal isomerization of linear butenes was studied. Assignment of OH groups observed in FTIR analysis is addressed taking into account previous NMR and computational studies regarding the FER structure. Possible previous termlocationsnext term of alkali ions in the zeolite framework are discussed. Close structure activity relationship has been observed between Bronsted previous termacid sitesnext term located in the 10 member ring (MR) channels and selective isobutene formation. Molecular dynamics (MD) calculations of possible products observed during n-butene transformation at reaction temperatures support the experimental findings.