U. Izquierdo

Levulinic acid hydrogenolysis on Al2O3-based Ni-Cu bimetallic catalysts

Abstract Inexpensive γ-alumina-based nickel-copper bimetallic catalysts were studied for the hydrogenolysis of levulinic acid, a key platform molecule for biomass conversion to biofuels and other valued chemicals, into γ-valerolactone as a first step towards the production of 2-methyltetrahydrofurane. The activities of both monometallic and bimetallic catalysts were tested. Their textural and chemical characteristics were determined by nitrogen physisorption, elemental analysis, temperature- programmed ammonia desorption, and temperature-programmed reduction. The monometallic nickel catalyst showed high activity but the highest by-product production and significant amounts of carbon deposited on the catalyst surface. The copper monometallic catalyst showed the lowest activity but the lowest carbon deposition. The incorporation of the two metals generated a bimetallic catalyst that displayed a similar activity to that of the Ni monometallic catalyst and significantly low by-product and carbon contents, indicating the occurrence of important synergetic effects. The influence of the preparation method was also examined by studying impregnated- and sol-gel-derived bimetallic catalysts. A strong dependency on the preparation procedure and calcination temperature was observed. The highest activity per metal atom was achieved using the sol-gel-derived catalyst that was calcined at 450 °C. High reaction rates were achieved; the total levulinic acid conversion was obtained in less than 2 h of reaction time, yielding up to 96% γ-valerolactone, at operating temperature and pressure of 250 °C and 6.5 MPa hydrogen, respectively.

Oxidative steam reforming of methane over nickel catalysts supported on Al2O3–CeO2–La2O3

Nickel catalysts supported on Al2O3, Al2O3–CeO2, Al2O3–La2O3, and Al2O3–CeO2–La2O3 were synthesized via the sol–gel method in acidic solution. The influence of the chemical composition and textural properties of the catalysts on oxidative steam reforming of methane was studied. Methane, oxygen, nitrogen and steam were fed into a fixed bed reactor and tested under atmospheric pressure at 550 °C, with O/C ratio = 0.3, S/C ratio = 1.0, and WHSV = 170.8 h−1. During 6 h of reaction, methane conversion and hydrogen selectivity were determined. Although lanthanide oxides are known to have excellent features, the addition of ceria or lanthana did not improve the catalytic performance of the Ni/Al2O3 system. Nevertheless the addition of both dopants was needed to end up with a stable catalyst. Characterization results revealed a low crystallite size (40 A), a high fraction of accessible Ni0 species (73.6%), migration of nickel and ceria from the bulk to the surface during activity tests, and a very low amount of coke deposited (4.7 mg C per g catalyst) on the Ni/Al2O3–CeO2–La2O3 catalyst that resulted in high catalytic activity.

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.