M.A. Larrubia

A FT-IR study of the adsorption of indole, carbazole, benzothiophene, dibenzothiophene and 4,6-dibenzothiophene over solid adsorbents and catalysts

The adsorption of benzothiophene (BT), dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT), dibenzofuran (DBF), indole (IND) and carbazole (CARB) on alumina, zirconia and magnesia has been studied by IR spectroscopy. The main adsorption process is due to adsorption on Lewis sites or on acid–base pairs. On alumina the adsorption is strongest, desorption being not obtained above 723 K. BT also undergoes a transformation with likely the heteroaromatic ring opening. Adsorption of 4,6-DBT is definitely limited in extent likely due to steric hindrance. The N-containing compounds IND and CARB are adsorbed dissociatively with breaking of the NH bond.

An ultraviolet–visible–near infrared study of the electronic structure of oxide-supported vanadia–tungsta and vanadia–molybdena

Abstract The ultraviolet–visible–near IR spectra of a series of catalysts have been recorded and discussed. In particular bulk and alumina-, titania- and silica-supported V, W, and Mo oxides have been considered. Additionally mixed V–W and V–Mo-supported oxides have been investigated. The data show that, in agreement with vibrational data and other literature data, the oxides supported on silica are similar to the corresponding bulk oxides. In contrast, the spectra of the oxides supported on alumina and titania correspond to surface oxide species where the metal stays in a lower overall coordination with respect to the bulk oxides. Finally, the spectra show that only in the case of titania-supported oxides an electronic interaction between the supported metal oxide centers through the support conduction band is possible. This allows to justify on electronic bases the activating effect of titania for vanadia, vanadia–tungsta and vanadia–molybdena catalysts used in the hydrocarbon selective oxidation catalysis and for the selective catalytic reduction of nitrogen oxide by ammonia.

On the chemistry of ammonia over oxide catalysts: Fourier transform infrared study of ammonia, hydrazine and hydroxylamine adsorption over iron–titania catalyst

The adsorption and transformation of ammonia over Fe2O3/TiO2 catalyst has been investigated by FT-IR spectroscopy in vacuum at increasing temperature. Ammonia is first coordinated over Lewis sites and later undergoes hydrogen abstraction giving rise either to NH2 amide species or, to its dimeric form N2H4, hydrazine. Other species tentatively identified as imide NH and nitroxyl HNO are produced further. The comparison of the infrared spectra of the species arising from NH3 and N2H4 and NH2OH adsorbed over Fe2O3/TiO2 strongly suggests that N2H4 is an intermediate in NH3 oxidation to N2 over this catalyst. So ammonia is activated in the form of NH2 species for both SCR and SCO. Ammonium ion is detected only in traces at r.t. It seems consequently demonstrated that Brønsted acidity is not necessary for the appearance of SCR and SCO activity.

WO3/TiO2 catalysts: Morphological and structural properties

Titania-supported tungsten oxide catalysts with different W loadings up to 9 wt. % and calcined at different temperatures have been prepared and characterized. It is found that W hinders the initial sintering of anatase, providing thermal stability. The interaction of W with TiO2 and the amount of hydroxy groups present on the surface can limit diffusion, thus reducing the sintering rate.

Studies on Water and Ammonia Programmed Thermodesorption of Mixed M(III)-vanadyl Phosphates

Hydrated M(III)-vanadyl phosphates (M (III)=Mn, Fe, Ga, Al) have been prepared and studied for water and ammonia adsorption properties by TG/DTA, NH3 TPD, FTIR and XRD techniques. The compounds have the same tetragonal layered structure of VOPO4 ⋅2H2 O, but shorter interlayer distances. Ammonia adsorption leads to intercalation of large amounts (0.19–0.39 mol/mol) of base between the layers of the materials, without displacement of water. The ammoniated phases obtained from these compounds have interlayer distances shorter than that of the corresponding precursors. In this connection an interaction mechanism NH3 -host is proposed. Treated at 450°C the materials adsorb ammonia only on the external surface because of the large decrease of the interlayer distance that prevents NH3 from entering the interlayer space. All M(III)-vanadyl phosphates present a wide distribution of strength of ammonia adsorbing sites.

Biofiltration of fishpond effluents and accumulation of N-compounds (phycobiliproteins and mycosporine-like amino acids) versus C-compounds (polysaccharides) in Hydropuntia cornea (Rhodophyta)

The biofiltration capacity, biomass-yield and accumulation of N- and C-compounds of Hydropuntia cornea were analyzed. Algae were grown in different conditions for 28 d: outdoor and indoor, with or without fishpond effluents. N-uptake efficiency of these effluents was higher than 95% after 7 d both outdoors and indoors. N-enriched conditions reduced the extent of photoinhibition and increased the maximal quantum yield in H. cornea. The biomass-yield was higher in outdoor grown-algae after 7 d and decreased independently of the treatment after 28 d. N, acid polysaccharide (AP) and mycosporine-like amino acid (MAA)-yields decreased throughout the experiment in all conditions. The highest MAA-yield was observed in fishpond effluent outdoor-grown algae, indicating a positive effect of increased radiation on MAA accumulation. However, APs were higher under N-depleted conditions. The use of MAAs as UV-screening and antioxidants, and the use of AP as immunostimulants are discussed.

Nanofiber Alumina Supported Lean NOx Trap: Improved Sulfur Tolerance and NOx Reduction

NOx uptake and S resistance performance was studied over Pt–Ba and Pt–K lean NOx trap (LNT) catalysts, supported on “standard” Al2O3 and a nanofibrous Al2O3. The activity study was accompanied by TEM, XRD and H2 chemisorption characterization. The nanofibrous Al2O3-supported catalysts resulted in better performance. This included improved storage capacity, reduction efficiency during the regeneration phase, thermal stability and S-tolerance.

Catalytic activity in partial oxidation of methane and physico-chemical characterization of a VPO system obtained from boiler ash

Bottom ash from the combustion of fossil fuels contain a higher amount of vanadium. The recovery and the precipitation could be an attractive route for the synthesis of a catalytic system (VPO). The morphology and structure of the precursor and the final systems, calcined at different temperatures, obtained using bottom ash as raw material, have been assessed using different techniques. Both VPO-bulk system and supported on different silicas have been tested in the partial methane oxidation. The experimental results are comparable to those reported for catalyst systems and performed in similar conditions. The reactivity appears to be essentially related with the exposed sites and the contribution of catalyst surface.

A new use of boiler ash: recovery of vanadium as a catalytic VPO system

Abstract A VPO system was prepared from boiler-ash. VO(H2PO4)2 phase has been obtained at low temperature and characterized through a combination of techniques including TG-DTA analysis, X-ray powder diffraction and FT-Raman spectroscopy. The thermal decomposition of the precursor material gives a VO(PO3)2 and V(PO3)3 phase mixture. Supported and unsupported catalysts prepared were compared and contrasted in the partial oxidation of methane (POM). The catalysts were more selective to C2-hydrocarbons than a VPO catalyst prepared by the conventional method and studied in similar conditions. Thus, the selectivity to C1-oxygenates was similar, however, the selectivity to COx products was hindered. The observation that the precursor VO(H2PO4)2 obtained from boiler ash as recovery and precipitation of the vanadium can generate catalysts of low selectivity to total oxidation products might provide a useful insight into the design of a new series of high activity and high selectivity partial oxidation catalysts.

Reassessment of fuel‐oil‐ash: Synthesis and characterization of a vanadium‐phosphorus‐oxygen system

Bottom ashes from the combustion of fossil fuels contain a high amount of vanadium. The recovery and the precipitation might be an attractive route for the synthesis of a catalytic system (VPO). The morphology and structure of the precursor and the final systems, calcined at different temperatures, obtained using bottom ash as raw material, have been assessed using a combination of scanning electron microscopy (SEM), thermal analysis (TG‐DTA), X‐ray diffraction (DRX) and Laser Raman Spectroscopy (LRS).