Juan C. Yori

Redox properties and catalytic activity of SO42−ZrO2 catalysts for n-butane isomerization Role of transition metal cation promoters

Abstract SO 4 2− ZrO 2 catalysts promoted with cations of transition metals (Fe, Cu, Ni, W, Pt, Co, Zn, Cd, Cr) were studied. Their influence on the catalytic activity for the isomerization of n -butane was analyzed in the presence of electron donor (H 2 ) and electron acceptor (O 2 , CO 2 ) gases. A new reaction scheme accounts for the one electron properties of the sulfate-zirconia catalyst. Transition metal cations are postulated to enhance activity through d -orbital interaction. Cations with a complete d level inhibit activity, but the presence of electron acceptor molecules (O 2 and CO 2 ) in the reacting medium attenuated this deleterious effect.

n-butane isomerization on tungsten oxide supported on zirconia

Abstract Tungsten oxide supported on zirconia catalysts prepared from ammonium metatungstate as a precursor and using different preparation routes were tested for n-butane isomerization at atmospheric pressure, 300°C, WHSV=1 h−1 and H2/nC4=6. The diffusion of polytungstates through the pores of Zr(OH)4 is sterically hindered due to the size of the anion. As a result of this, low penetration and the agglomeration in pore mouth are possible. The obtention and further utilization of polytungstates with a lower number of W atoms improve the distributions of W on ZrO2 surface and the catalytic activity. After calcination at 800°C, the better WO3/ZrO2 catalyst showed a catalytic performance similar to sulfated zirconia calcined at 620°C and corresponded to a material with well dispersed W. The more dispersed and active catalyst was obtained with an ammonium metatungstate solution stabilized 7 days at pH 6 before Zr(OH)4 impregnation, containing 15% W.

n-Butane isomerization on Pt/WO3–ZrO2: effect of the Pt incorporation

Abstract WO 3 –ZrO 2 catalysts for n -butane isomerization were prepared by several different procedures. The influence of a Pt promotor on catalyst activity and selectivity was investigated. Possible Pt–W interactions were particularly studied. It was found that Pt strongly interacted with the WO 3 –ZrO 2 support, which impeded reducibility and decreased H 2 chemisorption capacity and dehydrogenation activity. At low Pt content hydrogenolytic activity and H 2 chemisorption were absent. The interaction depends on the distribution of WO 3 on the ZrO 2 surface. The preparation conditions such as time of stabilization of the WO 3 precursor solution and the type of precursor used are very important for the catalytic activity. For Pt/WO 3 –ZrO 2 , there was no correlation between H 2 chemisorption at room temperature, cyclohexane dehydrogenating activity and the capacity to dehydrogenate n -C 4 . This is due to the fact that the three measurements are performed at different temperatures, with quite different reaction rates and thermodynamic feasibilities.

Influence of the crystalline structure of ZrO2 on the metallic properties of Pt in Pt/WO3–ZrO2 catalysts

The influence of the crystalline structure of ZrO2 on the metallic properties of Pt, when supported on WO3–ZrO2, was studied. Pt supported on tetragonal zirconia loses its metallic properties while when supported on monoclinic zirconia it presents good metallic activities. WO2,2- deposited on amorphous Zr(OH)4 before calcination generates an active material for n‐butane isomerization. The larger the fraction of the tetragonal phase of zirconia in this material, the higher the isomerization activity and the lower the metallic activity of Pt.

n-Butane isomerization on solid superacids

Abstract n-Butane isomerization reaction was studied on H-mordenite and ZrO 2 treated with sulphate ion. ZrO 2 /SO = 4 was calcined at different temperatures ranging 773–933 K; when calcining at 893 K, an optimum in catalytic activity was found. Both catalysts isomerize n-butane in different ways. On H-mordenite, disproportionation and cracking reactions occur simultaneously with isomerization. On the other hand, ZrO 2 /SO = 4 is a very selective catalyst for iso-butane formation, being the other reactions less favored. Differences in acid strength distribution can be mentioned to explain different catalyst behaviours. Catalysts deactivate with time on stream due to coke formation; H-mordenite activity diminishes continuously, and ZrO 2 /SO = 4 reaches a steady state.

Alkane isomerization on MoO3/ZrO2 catalysts

Molybdenum was used as an alternative to sulfate as promoter of zirconia for alkane isomerization reactions. It has similar effects to sulfate, tungstate and phosphate ions, modifying the physicochemical properties of unpromoted zirconia. Mo‐promoted zirconia catalysts do not show any activity for n‐C4 isomerization. For n‐C7 isomerization, the catalytic activity depends on Mo content, crystalline structure of the support and the molybdenum oxospecies present on the surface of the catalysts.

Production of bioethanol from carrot discards.

A revalorization of discarded carrots as substrate for the production of second-generation ethanol is proposed. In order to increase the fermentable sugar concentration of the musts two strategies were studied: Strategy 1 consisted in the enzymatic hydrolysis of bagasse must and Strategy 2 by which carrots were milled, dropped into distilled water and hydrolyzed with different enzymes prior to compressing and filtering to obtain carrot must. By applying Strategy 2 using 0.05% (v/v) of the enzyme Optimase CX255 at 70°C and pH 5.5 during 2.5h, the fermentable sugars extracted increased 3.5 times. In this way, the production of 77.5L of ethanol for each ton of discarded carrots was achieved. This process yielded bagasse as byproduct, which could be used for animal feed.

Surface acidity, catalytic activity and selectivity of some oxides supported on alumina

Abstract SiO2/Al2O3, MgO/Al2O3 and TiO2/Al2O3 catalysts of different composition, prepared by impregnation of alumina, were tested for 1-butanol and 1-butene reactions. Acidity measurements of the catalysts were carried out using the ammonia adsorption-desorption method. From the acidic sites of the catalysts, while 1-butene isomerization required a certain ratio of strong/total acidic sites to proceed. The stronger acidic sites were weakened and deactivated by the adsorption of 1-butanol and water.

H3PW12O40 (HPA), an efficient and reusable catalyst for biodiesel production related reactions: esterification of oleic acid and etherification of glycerol

In esterification of oleic acid with methanol at 25 °C HPA displayed the highest activity. Moreover the HPA could be reused after being transformed into its cesium salt. In the reaction of etherification of glycerol HPA and Amberlyst 35W showed similar initial activity levels. The results of acid properties demonstrate that HPA is a strong protonic acid and that both surface and bulk protons contribute to the acidity. Because of its strong affinity for polar compounds, HPA is also seemingly dissolved in both oleic acid and methanol. The reaction in this case proceeds with the catalyst in the homogenous phase.

Influence of platinum and hydrogen on n-butane isomerization on H-Mordenite

Hydrogen inhibits n-butane isomerization of H-MOR and improves catalyst stability and selectivity. Similarly, when Pt is present, hydrogen inhibits the reaction which is always controlled by the acid function.