J.A. Rob van Veen

A 57CO Mössbauer emission spectrometric study of some supported CoMo hydrodesulfurization catalysts

A suite of 11 CoMo/Al2O3 (and one COMO/SiO2) catalysts has been prepared employing four preparation routes, viz. one sequential-impregnation route and three different coimpregnation routes. Speciation of the Co present in the oxidic precursors (octahedral vs tetrahedral Co) and in the activated, sulfided catalysts (CoMoS, Co9S8, and unsulfided Co) was effected with the aid of 57Co Mossbauer emission spectroscopy (MES). A linear relation between the thiophene-hydrodesulfurization (HDS) activity and wt% Co-in-CoMoS was observed for each preparation route, but no unique correlation was found to exist. This was traced to the fact that the preparation routes differ in the amount of CoMoS I and CoMoS II they produce in the activated catalyst. Although these two phases differ in specific activity, CoMoS 11 being twice as active in thiophene HDS as CoMoS I, they cannot be distinguished on the basis of their Mossbauer parameters. It appears that octahedral Co is easier to sulfide than tetrahedral Co, but a substantial fraction of the latter is also found to be capable of entering CoMoS upon sulfidation. The reduced effectiveness of high-loading catalysts is traced to their being prone to COMoO4 formation in the calcination step. A rationalization of this behavior is offered.

Action of solvents on coal at low temperatures: 1. Low-rank coals

The dissolution behaviour of brown coals (67–75% C, daf) in pyridine, primary amines and aqueous KOH has been studied. The solubility in the last two solvents greatly depends on temperature, but in the first it is relatively temperature-independent. Pretreatment of the brown coals with aqueous HCl or with sodium ethanolate in ethanol leads to enhanced solubility. It is concluded that ester-bond breaking is necessary before extensive dissolution can take place. The solubility of brown coals in amines and aqueous KOH is found to increase with increasing carboxylic-acid group concentration in the coal. The solubility of Morwell brown coal in n-alkylamines at 180 °C increases with increasing length of the alkylchain in the solvent. The class of good solvents for brown coals is restricted to strong bases, because: 1. ester bonds have to be broken, 2. the acidic coal fragments have to be solubilized. Because of their capacity to break ester bonds these are so-called reactive solvents. Complete solvent recovery is impossible in the case of amines.

Large pore REE/Al pillared bentonites: Preparation, structural aspects and catalytic properties

CeAl and LaAl pillared bentonites were prepared by cation-exchange of different bentonites with hydrothermally treated (130–160°C for 16–136 h) solutions containing mixtures of aluminiumchlorohydrate (ACH) and REE (Ce and La)-salts. After calcination at 500°C the pillared clays are characterised by basal spacings of 24.8–25.7 A, and have BET surface areas of approximately 430 m2/g. The pillared products are hydrothermally stable to at least 500°C. The large basal spacings and surface areas are due to the formation of large REE/Al containing polyoxycations. The formation of this cation is favoured by high initial Al concentrations (≥3.7 M) and an OHAl molar ratio of approximately 2.5. CeAl or LaAl ratios can be as low as 130. Hydroconversion of n-heptane indicated that the activity of these materials is higher than that of a conventional Pt loaded amorphous silica alumina (ASA) reference catalyst. The selectivity is strongly dependant on the type of starting clay. In industrial hydrocracking of normal feedstock, a NiW loaded REE/Al pillared clay catalyst showed slightly higher initial activity than the ASA reference catalyst. However, the pillared clay catalyst showed rapid deactivation due to coke-formation, which reduced the surface area and pore volume. Additionally coke formation may be facilitated by the relatively high iron content of the pillared bentonite (3.43 wt%).

A real support effect on the activity of fully sulphided CoMoS for the hydrodesulphurization of thiophene

It is shown that on Al2O3, SiO2, and C, a fully sulphided CoMoS phase can be prepared with similar degrees of dispersion, and that the specific activity of this phase for the hydrodesulphurization of thiophene is higher when this phase is supported on carbon than when it is supported on alumina or silica.

The action of solvents on coal at low temperatures: 2. Medium- and high-rank coals

Abstract The dissolution behaviour of three medium-rank and three high-rank coals in various solvents has been studied. Aqueous KOH is a non-solvent up to 180 °C. Dissolution of medium-rank coals into aliphatic amines and pyridine is not influenced by mass transfer effects in the 120–180 °C temperature range-although it is at room temperature-and does not involve the breaking of chemical bonds. This sets them apart from low-rank coals, where ester bonds have to be broken before dissolution can take place. An extraction limit of ≈50% seems to exist. Of the solvents studied, nonoethanolamine is the best for low-rank bituminous coals but rather poor for higher-rank coals, while the reverse is true of pyridine. Extract yields in hexylamine and ethylenediamine remain approximately constant in the medium-rank range. Low-volatile bituminous coals and semi-anthracites still contain some soluble matter, the extraction of which is diffusion-limited, at least up to 180 °C. From the results a hypothesis concerning the basic physical constitution of coal is derived and a model of the coalification process rationalizing the conjectured changes in constitution with rank is suggested.

Comments on : Enhanced thermal stability of Al-pillared smectites modified with Ce and La by J.L. Valverde, P. Canizares, M.R. Sun Kou, and C.B. Molina

Valverde et al. (2000) recently reported on the preparation and characterization of Al-pillared smectites modified with Ce and La. Pillaring of clays with Al polyoxocations (Keggin type Al13) and a large variety of other complexing cations has been reported many times since the seventies. McCauley (1988) described in a patent the preparation of thermally stable pillared clays with large basal spacings of ~28 A , followed by publications by Sterte (1991a, 1991b) and Booij and coworkers (Booij et al., 1996a, 1996b). These authors used hydrothermally treated or refluxed solutions containing the Al polyoxocation and the rare earth elements in the form of their chloride salts. The presence of cerium or lanthanum seems to promote polymerization of the Al polyoxocation. Until now however, nobody has been able to assess the structure of the newly formed pillaring molecules. Although the inter-layer spacing is about twice that of the normal Al-pillared clay, chemical analyses indicate smaller amounts of Ce and La than expected from polymerization of the Al polymer alone. Several other studies on the combination of Al pillars with Ce or La resulted in the formation of pillared clays with basal spacings characteristic of Al-pillared clays. However, catalytic activity is enhanced owing to Ce or La ( e.g., Gonzalez et al., 1992; Mendioroz et al., 1993; Trillo et al., 1993). Unfortunately, Valverde and coworkers (Valverde et al., 2000) missed most …