Antonio Iannibello

On the role of phosphate anion in the MoO3-Al2O3 based catalysts

The incorporation of phosphate ion into -A12O3 was studied by chromatographic techniques. Phosphate ion strongly interacts with alumina through a mechanism in-volving surface basic sites; it competes with molybdate in the adsorption onto alumina and, when it is the first to be added, it limits the amount of Mo(V1) which can be adsorbed.The study of the phase transitions of alumina in the range 673-1323 K evidenced a stabilizing effect of phosphate. As phosphorus content increases, the isomerization activity of -A12O3 decreases in parallel with the adsorption of Mo(VI). In the Mo03-A12O3 systems, the hydrogen activation properties are strongly promoted by the presence of phosphate. These results are rationalized by hypothesizing the presence on y-alumina of strained Al-O-Al groups which have the character of Lewis conjugated acid-base sites and are responsible for adsorption properties, nucleation of a-alumina and catalytic activity. The role of phosphate is unique in stabilizing and/or deactivating these strained sites.

Phase transitions and surface stability of the WO3γ-Al2O3 system

Abstract The solid state transitions of the WO3γ-Al2O3 system have been investigated in the temperature range 873–1323 K. The formation of α-Al2O3 and Al2(WO4)3 phases and the thermal desorption of W(VI) attached to the γ-Al2O3 surface have been studied as function of the treatment time. The inhibition of the phase transition to α-Al2O3 and therefore the stabilization of the surface has been observed at 1323 K for samples with 7% WO3 content. This stabilization is critically affected by the tungsten content. An explanation for the stabilization of the alumina surface is proposed.

Spectroscopic study of the structure of chromium(VI), molybdenum(VI) and tungsten(VI) oxospecies anchored on aluminium oxide

Diffuse reflectance in the ultraviolet–visible and Raman spectra indicate that CrVI anchored to the Al2O3 surface by ‘pulse-’ and ‘step-’ addition methods is in a monomeric form both before and after activation. Monomeric MoVI and WVI oxospecies are also the most probable products on both freshly exchanged and activated dilute samples. On more concentrated samples spectral modifications occur which can be understood without invoking polymerization effects.

Bauxite-based catalysts in heavy crude oil hydrotreating

Abstract In hydrotreating heavy crudes, shale oils and coal liquefaction products, the cost of the catalyst is expected to be a critical factor in the process economy. This is due to non-volatile metal components in the feedstocks which cause high catalyst consumption. In a systematic study of the use of natural bauxite as carrier for low cost hydrotreating catalysts, the catalytic performance of bauxite-based catalysts in hydrotreating a 60% reduced crude from the Adriatic Sea region has been determined in a trickle-bed reactor. The following systems have been considered: MoO 3 /bauxite, WO 3 /bauxite, CoO-MoO 3 /bauxite, NiO-MoO 3 bauxite, NiO-WO 3 /bauxite. Data on a commercial catalyst,containing 4 and 12 wt % of CoO and MoO 3 respectively, are included for comparison. For maximum surface dispersion of the active components, Mo(VI) and W(VI) were incorporated on bauxite by anionic exchange. The Mo(VI) and W(VI) contents of the catalysts (6.6 wt % MoO 3 and 11.6 wt % WO 3 ) correspond to the chemisorption capacity of the natural material (after thermal activation). The catalytic properties of the bauxite-based catalysts resemble those of alumina-based catalysts. The synergistic effect of cobalt and nickel on molybdenum and tungsten in hydrodesulfurization (HDS) is evident. Tungsten-based catalysts are less active than molybdenum-based systems, in accordance with literature data. The lower activity of all bauxite-based catalysts, compared with the commercial CoO-MoO 3 -a1umina system, is attributed to differences in composition and surface properties. All of the catalysts examined promoted the production of a low boiling fraction in similar amounts, i.e., all catalytic systems show similar cracking activity. However, hydrogen uptake, as measured by the increase of the H/C ratio of the product, is substantially different and suggests large differences in the hydrogen-ating activity of the catalysts. Activity in hydrodenitrogenation (HDN) is lower than in HDS. Also the nitrogen removal properties of bauxite-based catalysts are comparable with the alumina-based systems. Differences in the kinetic steps involved in the HDS and HDN processes have been proposed; the experimental data indicate that the nitrogen removal process takes place through a number of kinetically important steps and this is consistent with the reaction network proposed for the HDN of model compounds. In metal removal, bauxite-based catalysts exhibit about the same activity as the commercial catalyst; this result is attributable to the relevant role played in this reaction by the pore structure of the support. These data show that, by the use of appropriate evaluation criteria, natural minerals, such as bauxites, can be selected to prepare efficient hydrotreating catalysts and that the activity and selectivity of these systems can be, to a certain extent, adjusted by a proper choice of chemical composition.

Use of supported rhodium and cobalt carbonyls as catalysts for the CO+H2 reaction effect of the support and the metal

The use of cobalt and rhodium catalysts derived from carbonyl clusters and supported on Al2O3, Al2O3–ZnO, ZrO2 and SiO2 for the CO + H2 reaction has been investigated. Only Rh-containing catalysts were active in the formation of oxygenated compounds (essentially ethanol). In all the runs the selectivity to methane plus ethanol was > 90%. The ratios of the rates of ethanol and methane formation or the rate of ethanol formation and the CO reaction reach a maximum when equal amounts of Rh and Co are present on the catalyst surface. Cobalt alone does not form oxygenates, but when mixed with rhodium it increases the selectivity to ethanol.

A Study of the Chemisorption of Chromium(VI), Molybdenum(VI) and Tungsten (VI) Onto γ-Alumina

In the pulse and step addition of ammonium dichromate, ammonium paramolybdate and ammonium paratungstate solutions to γ-alumina a large increase of the pH was observed in the liquid phase which suggests a common mechanism of interaction with the basic sites of γ-alumina. This mechanism involves the decondensation of the isopolyanion in the presence of alumina followed by the chemisorption of monomeric species. The most relevant difference between the three metal ions is the limiting amount of the chemisorbed oxospecies on γ-alumina: CrO 3 3. 28; MoO 3 7. 72; WO 3 19. 2 wt. %. The electronic and Raman spectra of the chemisorbed molybdenum(VI) and tungsten(VI) at low coverage can be interpreted as due to oxospecies in tetrahedral co-ordination. The relevance of the adsorption phenomena in the preparation of the commercial catalyst is finally pointed out.

Activity Of Iron-Rich Bauxite In The Hydrotreating Of A Heavy Petroleum Residue

A sample of bauxite, containing 28% Fe 2 O 3 , was activated by hydrothermal treating and molybdenum impregnation, and tested as a catalyst in the hydro-treating of a heavy petroleum residue in a bench-scale trickle-bed reactor. The thermally treated bauxite exhibited a significant demetalation activity, attributable to iron sulfide. After addition of a small amount of molybdenum (4.7% MoO 3 ) to the activated bauxite, hydrodesulfurization was strongly promoted. At highest conversion, hydrogen consumption was less than 100 Nm 3 /m 3 of oil. NMR analysis of the products showed a limited saturation of aromatic rings. Hydrocracking, significant in the presence of activated bauxite, was somewhat reduced by molybdenum addition.

Criteria For The Evaluation Of Bauxite As Carrier For Low-Cost Hydrotreating Catalysts

The determination of the porous structure after thermal activation, the measure of the anionic exchange capacity with respect to Mo(VI) and W(VI) species and the study of the functionality of the catalytic systems in model reactions have proved to be efficient criteria for a preliminary evaluation of natural materials as carriers for low-cost hydrotreating catalysts. Experiments performed with two bauxite samples, from a USA ore and a Southern Italian ore respectively, have made it possible to ascertain the possibility of utilizing the sample with lower iron content and higher surface area as a support for catalytic systems with properties comparable to those of more expensive alumina-based catalysts.