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Serum uric acid (sUA) has been associated with cardiovascular risk. Although the recent mechanistic hypothesis poses the basis for the association between sUA and left ventricular mass index (LVMi), the issue remains poorly investigated in a clinical setup. Through a retrospective analysis of the database of the departmental Hypertension Clinic of University Hospital of Salerno Medical School, we identified 177 essential hypertensives (age 60.3 ± 13.3 years; 85 men), free from uric acid-modulating medications and severe chronic kidney disease, and whose sUA values, anthropometric, clinical, and echocardiographic data were available. In the studied cohort, the average duration of hypertension was 8.4 ± 7.1 years. LVMi associated with classical determinants, such as age, blood pressure, and kidney function, although after multivariate correction, only age remained significant. Also, sUA correlated positively with LVMi, as well as body size, metabolism, and kidney function. In a multivariate analysis, sUA confirmed the independent association with LVMi. Also, levels of sUA >5.6 mg/dl are associated with larger cardiac size. We confirmed our data in a replicate analysis performed in a larger population (1,379 hypertensives) from an independent clinic. Our results demonstrate that sUA increases with LVMi, and a cutoff of 5.6 mg/dl predict larger LV sizes. Our data suggest that hyperuricemia might help to stratify the risk of larger cardiac size in hypertensives.

Samples of ammonium, protonic and potassium ferrierites were impregnated with tungsten species. The catalytic behavior of samples with and without tungsten during the linear butene isomerization reaction was studied. Tungsten loadings between 0.5 and 1.0% on ammonium ferrierite produce a synergetic effect both on activity and isobutene yield, while tungsten addition on the protonic form worsens the catalytic behavior of the unpromoted ferrierite. The presence of tungsten species on potassium ferrierite promotes the linear butene skeletal isomerization, with an optimum in the performance when the tungsten loading is between 3.5 and 4.0%. Tungsten species show a weak interaction with the potassium ferrierite surface. On the other hand, on protonic ferrierite the interaction is slightly stronger than on ammonium ferrierite, and the reduction of tungsten occurs practically in one step. The effect of both pretreatment and operational conditions over catalytic performance and deactivation of materials was also addressed. The higher the calcination temperature of ammonium ferrierite, the lower the linear butene conversion and the isobutene yield. Protonic ferrierite, tungsten promoted ammonium ferrierite, and tungsten promoted protonic ferrierite show similar qualitatively behaviors. After 5 min of reaction at any operational conditions, a high activity with low isobutene selectivity is observed. This behavior is related to the presence of strong acid sites. At long time-on-stream (TOS), the linear butene conversion at 450 °C is significantly higher than the one reached at 300 °C, while the isobutene yield remains between 12 and 18% for both reaction temperatures. Tungsten promoted potassium ferrierite samples display a different behavior. At 5 min the high activity is not reached, and both linear butene conversion and isobutene yield appear more stable with TOS; what is associated with the absence of strong acid sites. When reaction takes place at 450 °C, the isobutene yield significantly increases, approaching the yield obtained with the other samples. For all samples, the presence of hydrogen previously and during the reaction does not significantly modify the catalytic behavior, showing a small effect over the by-product distribution. By-products are formed from oligomers, which are among the products even at long TOS. The level of the carbonaceous deposit formed during reaction on protonic ferrierite, tungsten promoted ammonium ferrierite, and tungsten promoted protonic ferrierite was usually 6.0–7.8 wt.%. The oxidation profiles displayed two combustion peaks when the reaction took place at 300 °C, and only a high-temperature combustion peak when the reaction was carried out at 450 °C. On tungsten promoted potassium ferrierite, the deposit was considerably smaller (0.3–0.7 wt.%); coke formed at 300 °C showed a well-defined combustion peak at moderate temperature, while only a high-temperature combustion peak appeared when the deposit was formed at 450 °C. The amount of carbonaceous deposit is associated to the strength of acid sites while its nature is more strongly influenced by the reaction temperature.

The skeletal isomerization of linear butene on ferrierite, at atmospheric pressure and 0.15 atm 1-butene partial pressure, was studied by feeding 1-butene streams with different ethene and propene concentrations and exploring several operating conditions. At short time-on-stream (5 min), the strongest acid sites govern the catalytic behavior, independent of the operating conditions in the studied ranges. At longer times, the reaction temperature mainly defines the conversion level. The higher the temperature, the larger the linear butene conversion. Temperature also has a strong influence over the nature of the carbonaceous deposit formed during reaction. At 400 °C, the deposit mainly shows an aromatic nature. The presence of lower olefins as impurities in the feed modifies both catalytic activity and by-product distribution. By decreasing the ethene concentration, the C+ 5 fraction in the product stream increases and a lower carbonaceous deposit is formed. Using a nitrogen stream saturated with water during both pretreatment and reaction, the catalytic activity increases and the coke amount slightly diminishes, but the isobutene production is unfavored.

Deactivation of tungsten promoted ferrierite during the skeletal isomerization of 1-butene at 400°C, atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. Both potassium and ammonium ferrierites were impregnated with tungsten species using either tungstic acid or ammonium metatungstate as precursors, reaching loadings between 1.4 and 7.3%. After the tungsten addition on both ferrierite samples, neither the acid strength distribution nor the total acidity corresponding to the unpromoted materials change significantly. The strongest acid sites present on the ammonium ferrierite with and without tungsten and absent on the tungsten promoted potassium ferrierite, are responsible for the side-reactions. Deactivation of tungsten promoted ferrierites shows differences. Ammonium ferrierite with and without tungsten reach similar carbon contents, being larger than the ones obtained on potassium ferrierite with and without tungsten. In all cases, the carbonaceous deposit shows both olefinic and aromatic species, the proportion depending on the samples. Coke on tungsten promoted potassium ferrierite shows mainly an olefinic nature, while the deposit formed on tungsten promoted ammonium ferrierite has a more aromatic character. For the latter samples, the complete coke removal needs higher temperatures. The strength of acid sites determines not only the carbonaceous deposit amount but also its degree of condensation. The low isobutene selectivity at short time-on-stream (TOS) is avoided by starting the 1-butene feed with the catalytic bed at 200°C and then increasing temperature up to 400°C. It can be considered that a strong adsorption of reactant molecules takes place at low temperatures, thus deactivating the strongest acid sites.

The skeletal isomerization of 1-butene on ferrierite at 350°C and 400°C, atmospheric pressure and 0.14 atm 1-butene partial pressure is studied. The rapid decrease in activity with an increase in the isobutene selectivity is related to coke deposition. The carbon content is similar for both reaction temperatures. Temperature-programmed oxidation profiles of the used catalysts show two peaks for coke combustion, one each at low and high temperatures. The low-temperature peak is higher when reaction takes place at 350°C while the one at high temperatures is larger for reaction at 400°C. The carbonaceous deposits corresponding to the low-temperature combustion peak can be eliminated after stripping with a helium stream, suggesting that these deposits are rich in hydrogen. Diffuse-reflectance infrared spectroscopy measurements indicate that coke presents olefinic and aromatic character for all samples, being more olefinic after reaction at 350°C and more aromatic after reaction at 400°C. The presence of water during the treatment before the reaction changes the proportion of olefinic and aromatic coke formed. Regeneration under a nitrogen plus air stream at 660°C for 15 h allows almost complete elimination of the coke and full restoration of the catalytic activity to that of the fresh sample. However, the presence of a residual carbonaceous deposit (i.e. 0.9 wt.%) when starting the reaction, improves catalytic activity, isobutene yield and catalyst stability after some minutes on stream, as compared to the fresh sample. Therefore, we propose that the optimum regeneration procedure for ferrierite catalyst for n -butene isomerization consists of an oxidative treatment at high temperatures, but without the complete coke removal.

The effect of both total pressure and hydrogen partial pressure during the n-hexane isomerization on Pt/SO4 2™-ZrO2 at 200°C and 4 h™1 weight hourly space velocity was studied. Total pressure was varied between 1.0 and 10.0 kg cm-2; different hydrogen partial pressures were obtained by dilution with nitrogen keeping the total pressure at 6 kg cm-2. The n-hexane isomerization activity increases when increasing either total pressure or hydrogen partial pressure. Methylpentanes are the C6 isomers formed in major proportion and the 2-methylpentane/3-methylpentane ratio practically reaches the equilibrium value in most of cases. Isomerization is always accompanied by hydrocracking. Hydrogenolysis products were not observed, the main cracking products being propane, isobutane and isopentane; then, the cracking product distribution cannot be interpreted by considering an intramolecular rearrangement of carbocation intermediates. A slight deactivation takes place with time-on- stream. The lifetime of surface intermediates is longer in the absence of hydrogen or at a low hydrogen partial pressure; it allows oligomerization and cracking to prevail at short times and polymerization and coke formation at long times.

The influence of temperature, 1-butene partial pressure, weight hourly space velocity (WHSV), and pretreatment conditions on the activity, selectivity and stability of ferrierite during the 1-butene skeletal isomerization has been studied in order to understand the process of coke formation. Coke is characterized by temperature-programmed oxidation (TPO) and Fourier transform-infrared diffuse reflectance spectroscopy (DRIFTS). The catalytic behavior is strongly affected by the intrinsic properties of the zeolite, showing a significant deactivation associated with coke formation. The operational conditions, such as temperature, 1-butene partial pressure and WHSV, play an important role in the amount of coke produced, the temperature being the most important factor affecting the amount of coke. These conditions also modify the nature of the coke. A significant fraction of coke burns at temperature higher than 600°C.