Isomerization Of N-pentane Research Articles

Isomerization of n-pentane over La-Ni-S2O82−/ZrO2-Al2O3 solid superacid catalysts: Deactivation and regeneration

A La-Ni-S2O82−/ZrO2-Al2O3 (La-Ni-SZA) catalyst was prepared and studied in the isomerization of n-pentane. The mechanisms of deactivation and methods for regeneration of the La-Ni-SZA catalyst were explored. The results revealed that the yield of isopentane using fresh La-Ni-SZA was maintained above 65% in the first 1000min. However, the yield fell sharply from 65% to 25% during the subsequent 2000min. The decline in pentane isomerization activity was slow initially, but increased significantly after 1000min. The deactivation of the La-Ni-SZA catalyst may be due to a combination of carbon deposition, loss of Brønsted acidity, removal of sulfur entities. Based on this analysis, two regeneration methods were proposed. It was found that catalytic activity of the spent catalyst could be partially recovered (58%) by calcination. Resulfating the calcined catalyst with 0.5molL−1 (NH4)2S2O8 increased the acidity significantly, especially Brønsted acidity, compared with fresh catalyst. The isopentane yield using the resulfated La-Ni-SZA was maintained at about 58%, with isopentane selectivity above 90%, during the tested 3000min. Compared with fresh catalyst, the resulfated catalyst showed sustained excellent stability, although the initial activity was slightly lower. The improved stability of the resulfated catalyst can be explained by: (1) suppression of carbon deposition to some extent; (2) formation of improved acidic nature by resulfation, favoring isomerization on acidic sites; (3) restructuring of the acid and metal sites via the calcination-resulfation procedure.

Acid strength of Ni–S2O 8 2− /ZrO2 catalyst and its catalytic activity for n-pentane isomerization

A series of bifunctional Ni–S2O82−/ZrO2 (Nix-SSZ-T) catalysts with different Ni mass fraction (x, %) and calcintion temperature (T, °C) were prepared by impregnation method. The catalysts were characterized by XRD, FTIR, and py-FTIR. The effects of Ni content and calcination temperature on the acidic property and isomerization performance of catalyst were investigated using n-pentane isomerization as a probe reaction. The results show that the acidity of Nix-SSZ-T catalysts mainly derives from L acid. The addition of a suitable amount of Ni can induce the formation of more acid sites and in turn enhance the isomerization performance of Nix-SSZ-T catalyst. With increasing the calcination temperature from 550 to 700°C, B acid strength of catalyst weakens gradually, while the L acid strength increases first and then decreases. The Nix-SSZ-T catalyst with Ni content of 1 wt % and calcination temperature of 650°C exhibits the best isomerization performance. At reaction temperature of 230°C, pressure of 2. 0 MPa hydrogen /hydrocarbon molar ratio of 4: 1, and weight hourly space velocity (WHSV) of 1.0 h−1 the isopentane yield reaches 57.0%.

Hydroisomerization of n-Pentane over Pt/Mordenite Catalyst: Effect of Feed Composition and Process Conditions

The hydroisomerization of pure n-pentane over H-mordenite supported Pt-catalyst was investigated in a fixed bed reactor by changing reaction parameters such as temperature, pressure, and WHSV, as well as the H2/HC ratio. The maximum yield of isopentane over Pt/mordenite catalyst was achieved at 220 °C and a relatively low reaction pressure. To address the effect of feed composition on the catalytic performance of the samples, the catalysts were assessed for activity and selectivity in the isomerization of a mixture consisting of n-pentane (70 wt.%) and isopentane (30 wt.%) at 220 °C. The effects of pressure, WHSV, and H2/HC ratio on the catalyst performance were also studied using binary mixtures of the pentane isomers as a feedstock. It was observed that an effect of WHSV and H2/HC on the catalytic performance was similar to its behavior in pure n-pentane isomerization, while the conversion of n-pentane in the binary mixture showed a different trend and had a minimum value at 1.5 bar. It could be due to the presence of isopentane in feed and adsorption phenomenon of binary mixture on mordenite-supported catalyst.

The effect of Zn–Fe modified S2O8 2−/ZrO2–Al2O3 catalyst for n-pentane hydroisomerization

Fe–Zn-doped S2O82−/ZrO2–Al2O3 (SZA) catalysts were synthesized and characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared (FT–IR) measurements, hydrogen temperature-programmed reduction (H2–TPR), and pyridine infrared (Py–IR) measurements. The effects of Fe and Zn on the structure and isomerization performance of SZA were studied using n-pentane as a probe reaction. Results showed that all of the samples show the pure peaks of tetragonal ZrO2. The addition of Zn can improve the redox performance of the catalysts, while Fe can lead to a better dispersion of sulfate ions on the surface of the catalysts. As a result, an improvement in the redox performance of the Zn–Fe–SZA catalyst was observed. The Zn or Fe can increase mainly Lewis acidity of the SZA, and the total acidity of samples decrease in the following order: Zn–Fe–SZA > Zn–SZA > Fe–SZA > SZA. The Fe–Zn–SZA catalyst exhibits the best catalytic activity for n-pentane isomerization. The isopentane yield of the Zn–Fe–SZA catalyst reaches 67.2 % at 443 K, which is an increase of 44.2 % when compared with that found for SZA at its optimum temperature of 573 K.

Effect of Pd content on the isomerization performance over Pd-S2O8 2−/ZrO2-Al2O3 catalyst

The effect of Pd content on the performance of the Pd-S2O8 2−/ZrO2-Al2O3 solid superacid catalyst was studied using n-pentane isomerization as a probe reaction, and the catalysts were characterized by FTIR, BET, TG-DTA, H2-TPR, NH3-TPD and XPS. The results showed that an appropriate amount of Pd could promote the formation of acid sites, enhance the acidity of catalyst, improve the redox properties of the catalyst, and delay the decomposition of S2O8 2− effectively. The Pd-S2O8 2−/ZrO2-Al2O3 catalyst with 0.05 wt % Pd exhibited the best catalytic activity for n-pentane isomerization. At the reaction temperature of 200 °C, reaction pressure of 2.0 MPa, weight hourly space velocity of 1.0 h−1, H2/n-pentane molar ration of 4.0, the n-pentane conversion, iso-pentane selectivity and yield reached 61.1, 96.7, and 59.1 %, respectively, the isopentane yield with the Pd-S2O8 2−/ZrO2-Al2O3 increased by 39.1 % compared to S2O8 2−/ZrO2-Al2O3, and no obvious catalyst deactivation was observed within 100 h.

Effect of Al Content on the Isomerization Performance of Solid Superacid Pd–S2O82−/ZrO2 –Al2O3

The effect of Al content on the performance of the Pd–S2O82−/ZrO2–Al2O3 solid superacid catalyst was studied using n-pentane isomerization as a probe reaction. The catalysts were also characterized by X-ray diffraction (XRD), Fourier transform Infrared (FTIR), specific surface area measurements (BET), thermogravimetry–differential thermal analysis (TG–DTA), H2-temperature programmed reduction (TPR) and NH3 temperature-programmed desorption (NH3-TPD). The Pd–S2O82−/ZrO2–Al2O3 catalyst made from Al2O3 mass fraction of 2.5% exhibited the best performance and its catalytic activity increased by 44.0% compared with Pd–S2O82−/ZrO2. The isopentane yield reached 64.3% at a temperature of 238°C, a reaction pressure of 2.0MPa, a space velocity of 1.0h−1 and a H2/n-pentane molar ratio of 4.0. No obvious catalyst deactivation was observed within 100h.

Pt, Re and Pt–Re incorporation in sulfated zirconia as catalysts for n-pentane isomerization

Two groups of modified Sulfated Zirconia (SZ) catalysts were prepared by the sol–gel method. The first group was modified by four different concentrations of Pt metal (0.15, 0.30, 0.45 and 0.60wt%), whereas the second group contained Pt–Re combinations on SZ. All the prepared catalysts were characterized by XRD, TPR, TEM, TGA, IR spectroscopy as well as surface properties using the BET method. The catalytic activity of the catalysts was examined for the hydroisomerization of n-pentane to iso-pentane. The catalytic activity was found to increase with increasing Pt concentration in the monometallic catalysts. The combination of Re ion with Pt on SZ results in significant changes in the characters and activities of the catalysts. The 0.45wt%Pt+0.15wt%Re/SZ catalyst exhibited the highest selective compared to other metal ratios investigated.

Chromium oxide zirconia solid acid catalyst for n-pentane isomerization

New catalyst based on zirconia (ZrO2) supported by chromium oxide (CrO3) for isomerization of n-pentane was studied. CrO3-ZrO2 was prepared with chromium nitrate by the titration and sol-gel technique. The physical properties of the catalysts were characterized by XRD, BET surface area analyzer, and TEM. The acidity and structure of catalysts were determined by pyridine and lutidine preadsorbed FTIR spectroscopy. The isomerization of n-pentane was carried out at 523 K under hydrogen stream. CrO3-ZrO2 shows the differences in terms of physical properties where the introduction CrO3 partially eliminated the monoclinic phase of ZrO2 and developed new peaks assigned to tetragonal phase of ZrO2. CrO3-ZrO2 also shows a higher specific surface area where it increases in the pore volume of the catalyst compare to its parent zirconia. The IR results indicated that CrO3-ZrO2 catalyst have strong Lewis and weak Brønsted acid sites. The conversion of n-pentane for CrO3-ZrO2 was 32% respectively, while the selectivity to iso-pentane was 100%. ________________________________________GRAPHICAL ABSTRACT

Aluminum Fluoride‐Supported Platinum and Palladium as Highly Efficient Catalysts of n‐Pentane Hydroisomerization

AbstractCatalytic isomerization of n‐pentane was studied over novel high surface area (HS) aluminum fluoride supported palladium and platinum catalysts, prepared by the nonaqueous fluorolytic sol–gel synthesis. HS‐AlF3 maintained well its nanoscopic, mesoporous, and highly acidic character at higher temperatures, up to 350 °C. Both Pt/HS‐AlF3 and Pd/HS‐AlF3 catalysts, characterized by very small metal particle sizes (≈2 nm) maintained very good activity, stability, and selectivity towards isomerization (up to nearly 100 %) at up to 350 °C. Very strong acidity of HS‐AlF3 is the prerequisite for isomerization but the presence of the metal is also essential to maintain a high conversion level. The effect of metal–acid balance in Pd/HS‐AlF3 catalysts, important for bifunctional isomerization, was tested by screening three differently metal‐loaded catalysts. The performance of the 0.5 wt % Pd/HS‐AlF3 appeared as good as that of 2.0 wt % Pd. The properties of the HS‐AlF3 support, catalyst precursors, and catalysts were characterized by XRD, TEM, H2 chemisorption, and FTIR photoacustic spectroscopy of adsorbed pyridine, and NH3 temperature programmed desorption. The first three methods allowed evaluating the state of the metal in the reduced catalysts. The suppressed chemisorption of H2 must result from different factors, such as carbon presence in Pd introduced during catalyst synthesis and activation, metal–acidic support interaction, and, partially, metal encapsulation in AlF3 during sol–gel synthesis. Lewis and Brønsted acidity was detected in activated catalysts and both types of acid sites were assumed to play a role in bifunctional isomerization. NH3 effectively blocks the strongest acid sites and drastically limits the overall catalytic performance. Introduction of water to the reaction system also degrades, but to a lesser extent, the Pd(Pt)/HS‐AlF3 catalyst performance, most probably because of poisoning of only the strongest Lewis acid sites.

γ-Al<sub>2</sub>O<sub>3</sub> Supported SO<sub>4</sub><sup>2&#45</sup>/ZrO<sub>2</sub> Solid Superacid Catalysts for n-Pentane Isomerization

A solid superacid catalyst Pt-SO42-/ZrO2-A12O3 for n-pentane isomerization, was prepared by incipient-wetness impregnation. Preparetion conditions, namely, calcination temperature, concentration of sulfuric acid solution used in impregnation and Al2O3 concentration, were varied to investigate the effects on catalytic performance of Pt-SO42-/ZrO2-A12O3. The results showed that the PtSZA catalyst exhibited excellent catalytic performance for n-pentane isomerization. Under optimized preparation conditions of calcination temperature of 650°C, reaction time for 3 h, concentration of sulfuric acid solution for 0.5 mol/L, 30% of Al2O3 concentration and 0.3% of Pt concentration, the n-pentane conversion and isopentane selectivity of Pt-SO42-/ZrO2-A12O3 could reach up to 62.17% and 91.60%, respectively.

Synthesis of well-ordered SO42−/ZrO2-SiO2 materials in bi-acid system

A series of solid acid SO42−/ZrO2-SiO2 catalysts with a fixed Zr/Si molar ratio of 1.1 were successfully synthesized in one-pot through changing the H2SO4/HCl volume ratio during the self-assembly process. X-ray diffraction (XRD), UV-visible DRS, and high resolution transmission electron microscopy (HRTEM) results demonstrate that all the resultant catalysts exhibit a highly ordered 2D hexagonal mesostructures with zirconia particles of homogenously distributed tetragonal nanocrystallites in mesoporous walls. N2 adsorption and pyridine in-situ Fourier-transformed infrared spectra (FT-IR) further reveal that the surface area, pore volume, pore diameter and the relative strength of Lewis and Brønsted acidic sites of resultant catalysts can be controlled by tuning the H2SO4/HCl volume ratio during the synthesis. Different from pure mesoporous SBA-15 material, the mesoporous SO42−/ZrO2-SiO2 materials prepared in this work exhibit high structural stability and catalytic activity in n-pentane isomerization, which is attributed not only to hydrochloric acid that facilitates the formation of mesoporous silica but also to sulfuric acid that helps to stabilize the structure of catalysts and produce acid sites. The methods proposed in this work provide an important approach to synthesize ordered solid acid catalysts with high stability and potential applications in various acidic-catalyzed reactions.

Effect of iridium loading on the formation of protonic acid sites over Ir/Pt-HZSM5

The Ir/Pt-HZSM5 with different iridium loading (0.3-1.0 wt%) was prepared by impregnation of iridium on Pt-HZSM5. The acidic properties of Ir/Pt-HZSM5 were studied by FTIR spectroscopy, while the activity of the catalysts was tested for n-pentane isomerization in a microcatalytic pulse reactor.The IR results of adsorbed 2,6-lutidine showed that all catalysts possessed strong Brönsted and Lewis acid sites in the outgassing at 473 K and below.When Ir/Pt-HZSM5 was heated in hydrogen, protonic acid sites were formed with concomitant decrease of Lewis acid sites. An increase in iridiumloading continuously decreased the Lewis and Brönsted acid sites and inhibited the formation of protonic acid sites induced by hydrogen. The formationof protonic acid sites induced by hydrogen was also confirmed by the formation of electron detected by ESR spectroscopy. Additionally for n-pentaneisomerization, an increase in iridium loading decreased the yield of isopentane due to the inhibition in the formation of protonic acid sites via hydrogenspillover phenomenon.

Preparation and characterization of WOx/ZrO2 nanosized catalysts with high WOx dispersion threshold and acidity

WOx/ZrO2 nanosized catalysts with high dispersion threshold were prepared via a novel two-phase interface hydrolysis (TPIH) method and characterized by N2 physisorption, X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, Raman spectroscopy, and potentiometric titration with n-butylamine. It was found that the WOx/ZrO2 nanosized catalyst prepared by TPIH possessed a higher dispersion threshold (ca. 0.372g WOx/g ZrO2) than that obtained by a conventional impregnation method, due to its higher specific surface area of 114m2/g and tungsten surface density (6.2W atoms/nm2). Significantly, the catalyst at dispersion threshold by TPIH has a remarkable number of strong acid sites with E>400mV and nearly double catalytic activity for n-pentane isomerization compared to that prepared by a conventional impregnation method. When this is combined with the results of spectral characterization, the high activity of the catalysts obtained by TPIH is ascribed to the abundant strong acidic polytungstate species on ZrO2 at their dispersion threshold. Challenges for future work would be developing the TPIH method with supports and exploring reaction conditions to reduce coke formation.

Síntesis química, estudios de caracterización y reactividad de un material catalítico a base de ZrO2-H3PW12O40

In this work, the preparation and characterization of materials such as zirconium oxide (ZrO2) and phosphotungstic acid promoted zirconium oxide (ZrO2-H3PW12O40) is presented. Physico-chemical characterization results showed that addition of H3PW12O40 acted as both a textural and chemical promoter of zirconium oxide. The incorporation of phosphotungstic acid into the ZrO2 matrix delayed the sintering of the material and stabilized ZrO2 in the tetragonal phase. ZrO2 acidity was also enhanced, developing strong acid sites on its surface. The Pt/ZrO2-H3PW12O40 catalyst was active for n-pentane isomerization at 250 °C, exhibiting high selectivity to iso-pentane (95%). This result is probably due to its suitable acidity.

Ir/Pt-HZSM5 for n-pentane isomerization: Effect of Si/Al ratio and reaction optimization by response surface methodology

The effects of Si/Al ratio on the properties of Ir/Pt-HZSM5 and n-pentane isomerization were studied. XRD results indicated that the increasing Si/Al ratio increased the percentage crystallinity of the catalysts, whereas, FTIR results showed that the increasing Si/Al ratio decreased the number of strong Brönsted and Lewis acid sites which led to decrease the catalytic activity towards n-pentane isomerization. Ir/Pt-HZSM5 with Si/Al ratio of 23 showed highest activity towards n-pentane isomerization, and the operating condition was further optimized by using response surface methodology (RSM). The RSM experiments were designed by using face-centered central composite design (FCCCD) by applying 24 factorial points, 8 axial points and 2 replicates, with three response variables (n-pentane conversion, isopentane selectivity and isopentane yield). The Pareto chart indicated that the reaction temperature have largest effect for all responses. The optimum condition of n-pentane isomerization over Ir/Pt-HZSM5 was at treatment temperature of 723K, treatment time of 6h, reaction temperature of 548K and F/W of 500mlg−1min−1 in which the predicted value for the n-pentane conversion, isopentane selectivity and isopentane yield was 63.0%, 98.2% and 61.9%, respectively.

Pt-Mg-Ir/Al2O3 and Pt-Ir/HY zeolite catalysts for SRO of decalin. Influence of Ir content and support acidity

Pt-Ir/HY and Pt-Mg-Ir/Al2O3 catalysts were studied and tested in the reaction of ring opening of decalin. The acidity of the alumina support was modified by addition of 3% Mg and the acidity of the zeolite by ion exchange with NH4Cl. The Pt content of the catalysts was fixed at 1% (mass basis) while the Ir content was adjusted between 0.1 and 0.6%. The catalysts were characterized by temperature programmed reduction, temperature programmed desorption of pyridine and FTIR of adsorbed CO. They were further tested with the reactions of cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n-C5 isomerization.It was found that the Pt-Ir/HY catalyst was substantially more acid than Pt-Mg-Ir/Al2O3. Increasing the Ir content produced an increase of the hydrogenolytic activity and a decrease of the dehydrogenating activity of both catalysts. The n-pentane isomerization reaction results revealed that in the case of the alumina catalyst increasing the Ir content promoted both the catalyst stability and the cracking selectivity to C5 isomers. The opposite was found for the Pt-Ir/HY zeolite catalysts. The zeolite supported Pt-Ir catalysts performed better for decalin ring opening than those supported on alumina. Higher Ir content favored the formation of ring-opening products in all cases.

Sulfated Zirconia Catalysts for Low Temperature Isomerization of n-Pentane

UNCONVENTIONAL sulphated zirconia (SZ) catalysts were .….. prepared and examined for n-pentane isomerisation in this investigation. The sulfation was performed using H

Ir/Pt-HZSM5 for n-pentane isomerization: Effect of iridium loading on the properties and catalytic activity

The effects of iridium loading on the properties of Ir/Pt-HZSM5 and n-pentane isomerization were studied. XRD, IR, and NMR results indicated that increasing iridium loading did not much change the properties of catalysts, but eliminated the perturbed silanol groups at 3700 and 3520cm−1, whereas IR and ESR spectroscopy confirmed that increasing iridium loading continuously decreased the permanent Lewis and Brønsted acid sites and inhibited the formation of protonic acid sites induced by hydrogen. At low iridium loading (0–0.3wt%), cracking process proceed through dimerization-cracking step, whereas high iridium loading (0.5–2.0wt%) reduces the contribution of dimerization-cracking step and promotes the contribution of hydrogenolysis. The excessive amount of iridium loading, with the presence of a low amount of active protonic acid sites and hydrogen gas, accelerated the hydrogenolysis process. The activity of Ir/Pt-HZSM5 was marginal in the absence of hydrogen, showing the dependence of activity on promotive effect of hydrogen.

Interaction of Zn2+ with extraframework aluminum in HBEA zeolite and its role in enhancing n-pentane isomerization

The electrodeposition method was used to produce Zn2+ cation precursors, followed by the introduction of Zn2+ cation precursors to HBEA by the ion exchange technique. The introduction of Zn2+ cations slightly changed the specific surface area and crystallinity of HBEA. IR, XPS and solid state MAS NMR results showed that Zn2+ cations interacted with (AlO)+ extraframework aluminum to form Zn(OAl)2 and simultaneously induced the formation of bridging hydroxyl groups, Si(OH)Al. The pyridine adsorbed IR study revealed that the presence of Zn2+ cations fully eliminated weak and partially eliminated strong Brønsted acid sites. As a result, strong and relatively weak Lewis acid sites were formed in which the pyridine probe molecule desorbed at 623K and below. The presence of Zn2+ cations enhanced the catalytic activity of HBEA in n-pentane isomerization due to the presence of strong Lewis acid sites; the sites may facilitate the formation and maintenance of active protonic acid sites through a hydrogen spillover mechanism. At 598K, the yield of isopentane for Zn-HBEA was 25.7% higher than that of HBEA. Within a reaction temperature range of 373–648K, the apparent activation energy for isomerization of n-pentane over HBEA and Zn-HBEA was 118.76 and 90.79kJ/mol, respectively.

Negative effect of Ni on PtHY in n-pentane isomerization evidenced by IR and ESR studies

Ni/PtHY with different Ni loadings was prepared by impregnating HY with hexachloroplatinic acid solution and Ni 2+/N, N-dimethylformamide solution. An increase in the Ni loading decreased the crystallinity, specific surface area and meso-micropores of the catalysts. Ni interacted with hydroxyl groups to produce IR absorption bands at 3740–3500 cm −1. Increasing Ni loadings resulted in a decrease in the intensities of the broad bands at 3730-3500 cm −1 and the sharp band at 3740 cm −1 with simultaneous development of new absorbance band at 3700 cm −1 that was attributed to (–OH)Ni. The acidity of the samples did not significantly change with Ni loadings up to 1.0 wt%, which indicated that Ni mostly interacts with non-acidic silanol groups (terminal- and structural-defect OH groups). The presence of Ni decreased the activity of PtHY toward the isomerization of n-pentane because of a decrease in the number of active protonic-acid sites that formed from molecular hydrogen. IR and ESR studies confirmed that Pt facilitated the formation of protonic-acid sites from molecular hydrogen, whereas Ni, even when combined with Pt, didn't exhibit such ability. The absence of protonic-acid sites from molecular hydrogen significantly decreased the yield of iso-pentane and markedly increased the cracking products.