Carlos R. Vera

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.

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.

Adsorption in Biodiesel Refining - A Review

Biodiesel is a petrodiesel substitute composed of a mixture of fatty acid methyl esters obtained by the transesterification of plant oils or animal fats with short chain alcohols such as methanol or ethanol. Despite its natural origin biodiesel is technically fully compatible with petroleum diesel, requiring virtually no changes in the fuel distribution system or the Diesel motor. Its production and use have increased significantly in many countries and are in nascent status in many others. Other advantages of biodiesel compared to petrodiesel are reduction of most exhaust emissions, biodegradability, higher flash point, inherent lubricity and domestic origin (Chang et al., 1996; Romig & Spataru, 1996; Wang et al., 2000). Literature on the refining of biodiesel is abundant but concentrates almost exclusively on the transesterification steps for transforming fats and oils into esters of short alcohols and fatty acids. In this sense in the last years the most important advances in the reaction technology have been the development of continuous heterogeneous transesterification reactors (Bournay et al., 2005; Portilho et al., 2008) and the design of new robust non-catalytic processes for multifeedstock operation (Saka & Kusdiana, 2001; Saka & Minami, 2009). In the case of the refining operations downstream and upstream the transesterification reactors the biodiesel literature is however scarce. Two are the reasons for this: (i) Feedstock pretreatment in the case of biodiesel is a mature technology developed decades ago for the production of edible oil. (ii) After natural triglycerides are converted into fatty acid methyl esters, the product mixture needs little chemical adjustment since many properties of these esters are ideal for the functioning of Diesel motors. Some reports on post-reactor biodiesel refining have dealt with classical and simple techniques of purification, e.g. water washing (Karaosmanoglu et al., 1996). Others have indicated that adsorption technologies are particularly suited for the refining of biodiesel (Yori et al. 2007; Mazzieri et al., 2008; Manuale et al. 2011). In order to elucidate the role of adsorption processes in the refining of biodiesel, this review studies some theoretical and practical aspects related to the functioning, design and operation of adsorbers and their application to the purification of biodiesel product and feedstocks.

Preparation and characterization oF Ru-Sn/Al2O3 catalysts for the hydrogenation of fatty acid methyl esters

Ru-Sn/Al2O3 catalysts with different Sn loadings were prepared by the coimpregnation method. Several characterization techniques such as TPR, pyridine TPD and catalytic tests for dehydrogenation and hydrogenolysis were used to evaluate and compare such catalysts. TPR results indicate that Sn is deposited both onto the support and as species strongly interacting with Ru. Such non selective deposition modifies the acid and metallic functions of the catalysts. Both total acidity and acid strength distribution are affected: total acidity decreases and new sites of lower acid strength are created. Both dehydrogenating and hydrogenolytic activities are strongly diminished by the addition of Sn. Results of catalytic tests for methyl oleate hydrogenation indicate that methyl stearate is the main product, with only minute amounts of oleyl alcohol produced, and that the addition of Sn diminishes the hydrogenation activity.

Poisoning and regeneration of Pt-Pd/WO3-ZrO2 short paraffin isomerization catalysts

WO3-ZrO2 catalysts promoted with Pt and Pd were tested as paraffin isomerization catalysts using n-hexane as model compound. Sulfur and amine poisoning and regeneration tests were used to assess the impact of the addition of Pt and Pd on the deactivation resistance and regenerability. Pt and PtPd catalysts were the most active for n-hexane isomerization. The low activity of the Pd catalyst was attributed to poor Pd metal properties when supported over WO3-ZrO2 and to a decrease of the number of BrQnsted acid sites. PtPd was the only catalyst capable of full regeneration after S poisoning. Amine poisoning completely supressed the isomerization activity and the original activity could only be restored by calcination and reduction.

Low temperature ozone regeneration of oxoanion promoted zirconia catalysts for paraffin conversion

Abstract A regeneration scheme was tried which targeted a near isothermal operation of SO 4 2- -ZrO 2 catalysts for isomerization of n-butane: ozone regeneration at low temperature (150°C). A reaction-regeneration cycle in a pulse reactor was used to evaluate the properties of ozone and air for restoring the catalytic activity of the coked catalyst. Ozone was found to be able of burning the coke deposit over SO 4 2- -ZrO 2 to a great extent and an activity induction period after regeneration could be seen. Reaction (300°C) and regeneration (150°C) had a temperature gap in this system. On Fe-Mn promoted SO 4 2- -ZrO 2 a fully isothermal reaction-regeneration at 150°C was hypothetically possible but O 3 treatments did not restore the original activity, due to a destruction of the promotion action of Fe-Mn on the active sites.

Sulfur Resistance of Pt-W Catalysts

The sulfur resistance of low-loaded monometallic Pt catalysts and bimetallic Pt-W catalysts during the partial selective hydrogenation of styrene, a model compound of Pygas streams, was studied. The effect of metal impregnation sequence on the activity and selectivity was also evaluated. Catalysts were characterized by ICP, TPR, XRD, and XPS techniques. Catalytic tests with sulfur-free and sulfur-doped feeds were performed. All catalysts showed high selectivities (>98%) to ethylbenzene. Activity differences between the catalysts were mainly attributed to electronic effects due to the presence of different electron-rich species of Pt0 and electron-deficient species of . Pt0 promotes the cleavage of H2 while the adsorption of styrene. The catalyst successively impregnated with W and Pt (WPt/Al) was more active and sulfur resistant than the catalyst prepared with an inverse impregnation order (PtW/Al). The higher poison resistance of WPt/Al was attributed to both steric and electronic effects.

Coupling Solvent Extraction Units to Cyclic Adsorption Units

The possibility of regenerating the solvent of extraction units by cyclic adsorption was analyzed. This combination seems convenient when extraction is performed with a high solvent-to-impurity ratio, making other choices of solvent regeneration, typically distillation, unattractive. To our knowledge, the proposed regeneration scheme has not been considered before in the open literature. Basic relations were developed for continuous and discontinuous extraction/adsorption combinations. One example, deacidification of plant oil with alcohol, was studied in detail using separate experiments for measuring process parameters and simulation for predicting performance at different conditions. An activated carbon adsorbent was regenerated by thermal swing, making cyclic operation possible. When extracting the acid with methanol in a spray column, feed = 4 L min−1, solvent = 80 L min−1, feed impurity level 140 mmol L−1, and extract concentration 7.6 mmol L−1, the raffinate reaches a purity of 1.2 mmol L−1, the solvent being regenerated cyclically in the adsorber (364 kg) to an average of 0.7 mmol L−1. Regeneration of the solvent by cyclic adsorption had a low heat duty. Values of 174 kJ per litre of solvent compared well with the high values for vaporization of the whole extract phase (1011 kJ L−1).

NANOPARTICLES OF TUNGSTEN AS LOW-COST MONOMETALLIC CATALYST FOR SELECTIVE HYDROGENATION OF 3-HEXYNE

to be active and stereoselective for the production of (Z)-3-hexene, had the following order: 7.1WN/A > 8.5 WN/A ≥ 4.5 WN/A. Additionally, the performance of the synthesized xWN/A catalysts exhibited high sensitivity to temperature variation. In all cases, the maximum 3-hexyne total conversion and selectivity was achieved at 323 K. The performance of the catalysts was considered to be a consequence of two phenomena: a) the electronic effects, related to the high charge of W (+6), causing an intensive dipole moment in the hydrogen molecule (van der Waals forces) and leading to heterolytic bond rupture; the H+ and H- species generated approach a 3-hexyne adsorbate molecule and cause heterolytic rupture of the C≡C bond into C- = C+; and b) steric effects related to the high concentration of WO3 on 8.5WN/A that block the Al2O3 support. Catalyst deactivation was detected, starting at about 50 min of reaction time. Electrodeficient W 6+ species are responsible for the formation of green oil at the surface level, blocking pores and active sites of the catalyst, particularly at low reaction temperatures (293 and 303 K). The resulting best catalyst, 7.1WN/A, has low fabrication cost and high selectivity for (Z)-3-hexene (94%) at 323 K. This selectivity is comparable to that of the classical and more expensive industrial Lindlar catalyst (5 wt% Pd). The alumina supported tungsten catalysts are low-cost potential replacements for the Lindlar industrial catalyst. These catalysts could also be used for preparing bimetallic W-Pd catalysts for selective hydrogenation of terminal and non-terminal alkynes.