M.B. Güemez

Furfural production from xylose using sulfonic ion-exchange resins (Amberlyst) and simultaneous stripping with nitrogen

The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.

Aromatics hydrogenation on silica-alumina supported palladium-nickel catalysts

Abstract Nickel- and palladium–nickel catalysts supported on silica–alumina have been studied in the simultaneous hydrogenation of naphthalene and toluene. These catalysts were characterised by means of X-ray diffraction, CO chemisorption, temperature-programmed reduction, NH 3 temperature-programmed desorption, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO and X-ray photoelectron spectroscopy techniques. All the catalysts studied showed higher initial intrinsic activity in the hydrogenation of toluene than of naphthalene. Regarding the hydrogenation of toluene, the 1Pd–8Ni/SA sample displayed the strongest resistance to deactivation by coke precursors as compared with the Ni-free 1Pd/SA catalyst. For the 1Pd–8Ni catalyst, the characterisation data pointed not only to a high degree of reducibility of nickel but also the greatest exposure of Pd species. Both findings appear to be related to the development of nickel hydrosilicate species at the support interface. Indeed, a better resistance towards deactivation was obtained by Pd incorporation and by increasing Ni-loading.

Dibenzothiophene hydrodesulfurization on HY-zeolite-supported transition metal sulfide catalysts

Noble and semi-noble metals (Pt, Pd, Ru, Ir, Ni) were incorporated on a HY zeolite support, and tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Under steady-state conditions, the intrinsic activity of the catalysts was found to display the following order of reactivity: Ir>Pt>Pd≫Ni. While deactivation on Ir, Pt and Pd catalysts was very low, the significant differences in the activity of Ni and Ru zeolites could be attributed to catalyst deactivation. Temperature-programmed reduction studies revealed that noble metals were reduced at moderately low temperatures, whereas Ni catalyst was much more difficult to reduce as a consequence of the much stronger interaction with the zeolite substrate. For the most active Pt/HY and Ir/HY zeolites, photoelectron spectra of the used catalysts revealed that Pt is in metallic state (100% Pt°) and Ir is present as a mixture of metal (62% Ir°) and sulfide.

Furfural production from xylose + glucose feedings and simultaneous N2-stripping

The current furfural manufacturing process is based on homogeneous catalysts as well as steam as the stripping agent. Novel xylose-dehydration research studies include heterogeneous catalysts with high acidity and tailored selectivity. This work aims to evaluate the effect of additional glucose with the xylose feeding during simultaneous N2-stripping of furfural catalyzed by ion-exchange resins. Given the low batch performance of Amberlyst 70, the N2-stripping data showed high furfural yields and selectivity in the condensate stream. The different continuous feeding configurations showed that xylose/glucose ratios similar to the real pentosan-rich biomass could be fed achieving furfural yields of 75% at 200 °C. Moreover, the proposed study serves as a preliminary study to achieve high xylose conversion and relatively low glucose dehydration rates, showing its potential as a possible future process for the upgrading of carbohydrates to furan-based fuel additives.

Evaluation of silica-alumina-supported nickel catalysts in dibenzothiophene hydrodesulphurisation

Abstract The influence of both the nickel–support interaction and the Pd promotion on the activity and thiotolerance during the hydrodesulphurisation (HDS) of dibenzothiophene (DBT) was studied in a variety of amorphous silica-alumina-supported nickel catalysts (Ni/ASA). The catalysts were characterized by means of X-ray diffraction (XRD), N 2 adsorption–desorption measurements, temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of NH 3 , CO chemisorption and X-ray photoelectron spectroscopy (XPS) techniques. In the low-nickel-content catalysts, a difficulty in reducing the Ni 2+ –support phase was observed, whereas in the high nickel-content catalysts a major reducible NiO phase was developed. Catalysts containing low amounts of nickel exhibited higher activity and selectivity toward ring-opening (RO) products than those containing higher nickel loadings. The larger ring-opening activity and the greater resistance to deactivation of the low nickel-loading catalysts appear to be related to the morphology of the nickel phases at the catalyst surface, consisting of very small Ni clusters separated by non-reduced Ni 2+ species. The high activity of the catalysts in the ring-opening reaction can be explained assuming that non-reduced Ni 2+ species might to force DBT adsorption on Ni 0 phase via CC bonds perpendicular to the surface. In addition, the greater resistance of the catalysts to deactivation was related to H 2 S adsorption on Ni 2+ species, thus maintaining Ni 0 locations available for performing the ring-opening reaction.

Surface properties and hydrocracking activity of NiMo zeolite catalysts

The hydrocracking properties of Ni, Mo and NiMo sulphides supported on an ultrastable HY zeolite were examined by studying the hydroconversion of n-decane at moderate pressure (3 MPa). All catalysts were found to deactivate during the first hours on-stream, then reaching almost constant conversion values. Their cracking conversions are significantly higher than that of the HY support. A strong imbalance between the hydrogenation and the acidic function of catalysts was observed. The product selectivities did not depend on the conversion and the secondary cracking occurred. In the binary NiMo samples no synergetic effect between the individual Ni and Mo phases was observed. A reasonable correlation between the n-decane steady-state conversions at 598 K, the sulphidation degree of the metals and Bronsted acidities of catalysts were found.

Hydrodesulfurization over PdMo/HY zeolite catalysts

A series of palladium-promoted Mo catalysts was prepared by two-step impregnation procedure using an ultrastable HY zeolite carrier. The mutual effect of Pd and Mo phases and zeolitic support was investigated in hydrodesulfurization (HDS) of dibenzothiophene (DBT) and diesel oil (1.1 wt% S). Pd/HY was more active than its binary PdMo/HY counterparts, suggesting an inhibitory effect of Mo on Pd. The incorporation of Pd probably prevented deactivation of PdMo catalysts in HDS of DBT. The initial sulfur conversion in HDS of gas oil over Pd/HY was similar to that on a commercial CoMo/Al2O3 catalyst; however, both Pd/HY catalyst and the blank HY zeolite deactivated very fast at short times on-stream. On the basis of catalyst characterization by X-ray photoelectron spectroscopy, Fourier transform i.r. spectroscopy of adsorbed CO and pyridine, and temperature-programmed reduction, it is concluded that formation of HxMoS2 and S[PdH+] hydride-like species in PdMo zeolites are probably responsible for the inhibitory effect on HDS activity.

Glycerol conversion into H2 by steam reforming over Ni and PtNi catalysts supported on MgO modified γ-Al2O3

Abstract The glycerol catalytic steam reforming over Ni and PtNi catalysts to produce H 2 was studied. The activity results indicate that the catalyst with the lower content of MgO, the NiA1M, provides higher H 2 molar ratios than the Ni catalyst. The behaviour of the NiA1M catalysts seems to be related to the Ni o species stabilization by nickel-magnesia interactions, which are favoured by the presence of well dispersed MgAl 2 O 4 spinels. The bimetallic catalyst, PtNiA3M named, reforms the intermediate products improving the activity of the Ni monometallic catalyst toward H 2 production. The characterization results suggest that the Pt in the Ni monometallic catalyst enhances the Ni o particles dispersion and the nickel species reducibility by H 2 spillover.

Effect of fluorine on hydrodenitrogenation activity of doubly promoted (Zn + Co) molybdena-alumina catalysts

Abstract Activity for the hydrodenitrogenation (HDN) of quinoline has been studied at an overall pressure of 7 MPa in the temperature range 623–698 K, on a series of doubly promoted ZnCoMo catalysts supported on fluorinated alumina (0.0–2.0 wt% F). For the F free catalysts the partial substitution of Co by Zn does not affect HDN activity. However, for the fluorinated catalyst series, the HDN activity was found to increase slightly for fluorine contents around 1.0–1.3 wt% F. Simultaneously, a minimum in hydrogenation activity to N free products was observed. These results have been explained in terms of two antagonistic effects. While fluorine favours multilayered MoO 3 crystallites, with shorter dimensions in the lateral direction caused by disruption in the geometry, cobalt has a propensity to intercalate at the edges of the crystals, thus inhibiting the formation of stacks in which the reduced sites, believed to be needed for HDN and hydrogenation, are located.

Natural and synthetic iron oxides for hydrogen storage and purification

In this paper, the hydrogen storage capacity of some synthetic and natural iron oxides is presented. The results of the activity tests and characterization techniques of natural and synthetic iron oxides (N2 adsorption–desorption isotherms, temperature-programmed reduction, X-ray diffraction, and plasma atomic emission spectroscopy) suggest that the use of chromium on iron oxide systems improved their hydrogen storage capacity. This is related to the capacity of chromium to modify the iron oxide reduction profile when Cr was incorporated. A direct reduction from Fe3O4 to Fe was observed as the mechanism for H2 storage. In addition, natural oxides as commercial Superfine and Densinox-L oxides are proved to be suitable materials to store and purify H2 due to their high stability during different cycles of reduction and oxidation. The best results among the natural ones were Densinox-L and among the synthetic ones Fe–10Cr.