Cyclopentane Hydrogenolysis Research Articles

Influence of the Ir content and the support on the thiotolerance of the Ir/SiO2‐Al2O3 catalysts for selective ring opening of decalin

AbstractThe influence of Ir content on sulphur tolerance for the selective ring opening of decalin was investigated. Ir/SiO2‐Al2O3 catalysts (70 wt% and 80 wt% SiO2) were used. In the absence of sulphur, slight differences were observed on the yields according to the metallic content regardless of the support used. Although the results of cyclopentane hydrogenolysis showed that the metallic function acquires importance as the metal content increases, for these metal percentages the acid function limits the rate of decalin opening reaction. Products distribution are strongly modified using decalin with S content compared to pure decalin. The formation of dehydrogenated products is virtually null due to S adsorbed on the metal sites. The support has low influence on the thiotolerance. The results, related to the amount of S per Ir surface atom, showed that for a moderate S content (S/Irsurf ∼ 0.30), 1.5 Ir/Sy appears to be less poisoned than 1Ir/Sy and 2Ir/Sy.

Ru‐Pt catalysts supported on Al2O3 and SiO2─Al2O3 for the selective ring opening of naphthenes

AbstractAlumina and silica‐alumina supported Ru‐Pt catalysts were evaluated for the ring opening of naphthenes. Pt, Ru, and Ru‐Pt catalysts were prepared by the impregnation of inorganic precursors over γ‐alumina and silica‐alumina supports. The catalysts were evaluated by temperature programmed reduction (TPR), pyridine temperature programmed desorption (TPD), CO‐FTIR, and by test reactions of 33DM1B isomerization, cyclohexane dehydrogenation, cyclopentane hydrogenolysis, and the ring opening of decalin. The strong interaction between the metals (Pt‐Ru) was attributed to their reductions occurring simultaneously. The acidity and strength of the acid sites of the monometallic Ru catalyst were higher than those of the monometallic Pt catalyst. The total acidity (Lewis and Brønsted) and the strength of the acid sites were higher for the silica‐alumina supported catalysts. The silica‐alumina catalysts had 10 times more Brønsted acidity than the γ‐alumina ones and an increased activity and selectivity to decalin ring opening products. Supported monometallic Ru had the best performance for the ring opening reaction.

Selective hydrogenation of oleic acid to fatty alcohols on Rh-Sn-B/Al2O3 catalysts. Influence of Sn content

The influence of tin loading of Rh-Sn-B/γ-Al2O3 catalysts on the selective hydrogenation of oleic acid to fatty alcohol was studied. The catalysts were characterized by N2 sorptometry, temperature programmed reduction and X-ray photoelectron spectroscopy. Cyclohexane dehydrogenation and cyclopentane hydrogenolysis were also used to evaluate the metal function.Sn and Rh are in interaction since the conversion values of the cyclohexane, cyclopentane, and TPR profiles are modified by tin addition. Moreover, XPS analysis showed that Sn modifies the amount of Rh on the surface and its reduction state. The yield to oleyl alcohol was maximum for the Rh(1 wt%)-Sn(4 wt%)-B/γ-Al2O3 and Rh(1 wt%)-Sn(5 wt%)-B/γ-Al2O3 catalysts. This behavior could be explained considering that the Sn addition limits the Rh activity for hydrogenation of the CC double bond, thus increasing the formation of oleyl alcohol. At low Sn content, high selectivity to octadecane appears due to the total hydrogenation of the CC, COH and CO bonds.

Pt–Ir/Al2O3 catalysts for the ring opening of naphthenes. Performance as a function of time

The catalytic performance of a Pt–Ir/Al2O3 catalyst for the selective ring opening of decalin was studied as a function of time. Fresh and used catalysts were evaluated with the reaction tests of cyclohexane dehydrogenation and cyclopentane hydrogenolysis to assess the metal function properties. The transformation of decalin was used as a test reaction for the ring opening of naphthenes. For this test the yield to ring contraction products passed through a maximum at intermediate values of conversion while yields to dehydrogenation, ring opening, and cracking products increased with conversion. Coke deposition also increased with reaction time but its distribution on the metal and acid sites did not change. Coke was more toxic for hydrogenolysis than for de/hydrogenation and therefore the products ratio of (ring opening)/(dehydrogenation) decreased at end of the reaction. Higher yields to dehydrogenated products produced a higher coke deposition while high activity in both hydrogenolysis and dehydrogenation favored the ring opening reaction.

Study of the performance and stability in the dry reforming of methane of doped alumina supported iridium catalysts

Abstract Iridium catalysts supported on alumina doped with both alkaline (Na and K) and alkaline earth metals (Ba, Ca and Mg) of different concentrations (1, 5 and 10 wt%) were tested in the dry reforming of methane. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2 and 2-propanol dehydration. Catalysts were characterized by temperature-programmed reduction, TEM, XPS, cyclohexane dehydrogenation and cyclopentane hydrogenolysis. Dopants were showed to suppress the acidity of the support and the γ-Al2O3 phase remained in the supports doped with Ca, Ba, Na and K after calcination at 800 °C, whereas a phase transition to magnesium aluminate was found for magnesium doped alumina. Stability tests, using long time dry reforming reactions, showed that iridium catalysts have high sintering resistance, their metallic phases being very stable since neither carbon deposition nor sinterization processes were observed.

Influence of the metallic content on Pt-Ir/Nb2O5 catalysts for decalin selective ring opening

Ring opening of naphthenic rings on Pt-Ir catalysts supported on Nb2O5 was studied in this work. The catalysts were prepared by impregnation. In the case of the bimetallic catalyst, the total metallic load was kept constant while varying the individual quantity of impregnated Ir and Pt. The samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N2 sorption, NH3 TPD and model reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis). The decalin ring opening capacity of the catalysts was evaluated. Monometallic Ir and Pt catalysts as well as bimetallic catalysts were active towards cyclohexane dehydrogenation and cyclopentane hydrogenolysis. Regarding the bimetallic catalysts, an increase on the Pt content promoted the cyclohexane dehydrogenation while hindering the hydrogenolytic activity. In the selective ring opening of decalin, the bimetallic catalysts presented activities comparable to the monometallic catalysts. Nonetheless, Ir(0.3%)/Nb2O5 catalyst presented the highest selectivity towards ring opening products with the lowest selectivity towards dehydrogenated products.

Selective ring opening of methylcyclohexane and decalin over Rh–Pd supported catalysts: Effect of the preparation method

Bimetallic Rh–Pd catalysts prepared by various impregnation methods were evaluated in the selective ring-opening of decalin and methylcyclohexane (MCH) used as model molecules of hydrogenated aromatics of the Light Cycle Oil fraction. Rh and Pt were deposited on Al2O3 and SiO2–Al2O3 (S40) by coimpregnation (CI) or successive impregnations (SI) with different orders of metal addition. Catalysts were characterized by H2 chemisorption, temperature-programmed reduction, temperature-programmed desorption of pyridine, and test reactions of cyclopentane hydrogenolysis and isomerization of 3,3-dimethyl-1-butene. Their catalytic behaviors for the ring-opening reaction were deeply influenced by the acidity of the support, and in a lesser extent by the metal deposition method. On both supports, the CI catalysts, displaying the highest dispersion values, exhibited the best ring opening performances. In the case of the SI catalysts, the addition order of both metals modified in a moderate way the properties of the catalyst. The yield to ring opening products obtained in MCH ring opening with CI catalysts supported on Al2O3 was 39–69% higher than those prepared by SI (conversion=55–60%) while for the catalysts supported on S40, the yield to ring opening products was 8–48% higher for the CI catalysts compared to SI catalysts (conversion=72–77%). The conversion of decalin for the bimetallic catalysts supported on Al2O3 was lower than 20% being dehydrogenated compounds the main reaction products regardless the preparation method. The catalyst supported on S40 showed decalin conversion values between 46 –53% and yield to ring opening near to 30%. Moreover, the CI catalysts have yield to ring opening 10 to 20% higher than the catalysts prepared by SI. The catalyst prepared by coimpregnation supported on S40 was the most appropriate for opening the MCH and decalin due to an optimal balance between the metal and acid functions.

Influence of Time and Temperature on the Regeneration of PtReIn/Al2O3 Naphtha Reforming Catalysts

The influence of temperature (450–500 °C) and time (1–4 h) of coke combustion on the catalytic properties of PtReIn/Al2O3 were studied. The results of the cyclohexane dehydrogenation and cyclopentane hydrogenolysis reactions show that the regeneration treatment with diluted oxygen can fully recover the activity of the metal function despite some observed segregation of Re and In. In the case of the n-heptane reforming reaction, the regenerated catalysts had lower activity and stability than the fresh ones. The experiments at high temperature in air showed that In prevents the sintering of Pt and Re but at 650 °C a segregation of Re from the Pt–Re phase occurs.

Influence of Na content on the catalytic properties of Pt-Ir/Al2O3 catalysts for selective ring opening of decalin

The influence of the Na addition on Pt-Ir/Al2O3 on the reaction of selective ring opening of decalin and methyl cyclopentane was studied. The catalysts were evaluated by means of TPR, pyridine TPD, TEM, FTIR-CO and by the reaction tests of cyclohexane dehydrogenation, hydrogenolysis of cyclopentane, selective ring opening of decalin and methyl cyclopentane. It was found that Na strongly decreases the acidity and influences the metal properties of Pt-Ir/Al2O3 catalysts. The interaction between Pt and Ir is increased by the presence of Na, with larger metal crystals being obtained on the support modified by Na. As a consequence, the catalytic properties are also modified and the CP/CH ratio (parameter of demanding/not demanding reaction) is increased with sodium concentration. In the case of MCP reaction, Na strongly decreases the aromatic and n-C6 formation and favors the selective reaction mechanism, thus favoring the formation of 2MP and 3MP. For the decalin reaction, it was found that the yield to the dehydrogenated product of the catalysts supported on Al2O3-Na is lower than that of the free Na-alumina supported catalyst, whereas the opposite occurs with the yield to C1 due to the higher hydrogenolytic and lower dehydrogenation activity of the catalysts with Na. The yield to ring contraction (RC) products is higher on the catalyst without Na due to the higher acidity which favors the ring contraction reaction and the lower metallic activity; thus, the transformation of the RC product to ring opening products is decreased.

N-decane dehydrogenation on bimetallic PtSn and PtGe catalysts prepared by dip-coating

The catalytic performance of Pt, PtSn and PtGe supported on γ-Al2O3 (γ-A) deposited by dipcoating of spheres of α-Al2O3 (α-A) was studied in the n-decane dehydrogenation. The effect of Sn and Ge addition to Pt on the activity and selectivity was analyzed. The catalytic characterization was carried out using cyclohexane dehydrogenation (CHD), cyclopentane hydrogenolysis (CPH), temperature-programmed reduction (TPR), hydrogen chemisorption, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and scanning electronic microscopy (SEM). Pt(0.5)Sn/γ-A/α-A catalyst had the best catalytic performance and showed a low electronic interaction between the metals, with a surface segregation of Sn and the presence of oxidized Sn stabilized on the support. PtGe catalysts presented strong interactions with probable alloy formation. The catalytic performance of these catalysts is comparable to that reported in the patents.

N-Decane dehydrogenation on Pt, PtSn and PtGe supported on spinels prepared by different methods of synthesis

The catalytic performance of Pt, PtSn and PtGe supported on ZnAl2O4 obtained by mechanochemical synthesis (MS) or coprecipitation (COPR) is studied in the production of 1-decene from the n-decane dehydrogenation. The effect of preparation methods and Sn and Ge addition to Pt on the activity and selectivity was analyzed. The catalytic characterization was carried out by using XRD, Specific surface area, 2-propanol dehydration reaction, equilibrium pH, cyclohexane dehydrogenation (CHD), cyclopentane hydrogenolysis (CPH), TPR, H2 chemisorption, XPS, TPO, and TEM. Characterization studies indicate that the addition of Sn to the Pt metal phase modifies not only the catalytic properties, but deactivation and stability as well. PtSn catalysts on both spinels were more active, with lower activity fall than PtGe ones and the higher the Sn loading, the more noticeable this effect. Besides, PtSn catalysts supported on ZnAl2O4 MS showed a more stabilizing effect.

MgAl2O4 spinel prepared by mechanochemical synthesis used as a support of multimetallic catalysts for paraffin dehydrogenation

The catalytic performance in n-butane dehydrogenation of bimetallic PtSn, PtGa and PtIn, and trimetallic PtSnIn and PtSnGa catalysts (with low metal contents) supported on a MgAl2O4 prepared by a novel mechanochemical synthesis was evaluated both in flow and pulse equipment. The influence of the addition of different promoters (Sn, Ga and In) to Pt on the activity, selectivity and deactivation in the n-butane dehydrogenation reaction was studied. Stability experiments through successive reaction-regeneration cycles were carried out for selected catalysts. In order to correlate the properties of the metallic phase of the catalysts with the catalytic behavior, several characterization techniques were used, such as test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), TPR, XPS, H2 chemisorption and TEM. Bimetallic PtSn catalyst has a better catalytic behavior than PtIn and PtGa ones. For PtSnM (M: In or Ga) catalysts, whereas Ga addition to the bimetallic catalyst does not practically modify the dehydrogenation performance, the addition of In produces an increase of the activity and the selectivity to butenes. Characterization results indicate the presence of geometric effects for the PtSn catalyst, and geometric and electronic effects for PtIn and PtGa ones. For trimetallic catalysts, the presence of a close contact between Pt, Sn and In or Ga in both trimetallic catalysts was found, mainly due to geometric effects like blocking and dilution of the active sites by the promoters. In stability experiments, the trimetallic PtSnIn/MgAl2O4 catalyst clearly displays the best catalytic performance along reaction-regeneration cycles, though PtSnGa and PtSn catalysts also showed a very good behavior through the successive cycles. The characterization of these catalysts after cycles shows that their metallic phases are slightly modified along the cycles.

Influence of iridium content on the behavior of Pt-Ir/Al2O3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes

The influence of Ir content on the properties of Pt-Ir/Al2O3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes was studied. It was found that these catalysts display a strong Pt–Ir interaction but only a weak metal–support interaction. Catalyst acidities depend on the metal loading, but opposite effects were observed on alumina (decrease) or titania (increase) as the metal loading increased. The results obtained from test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis) showed that titania supported catalysts were less active than their alumina supported counterparts. This behavior could be due to the partial blockage of metallic sites by migrated TiOx species and the sinterization of metallic phase during the reduction step. The methylcyclopentane ring opening reaction was found to occur through a partially selective mechanism, and an increase in activity as the Ir loading increased was observed. The selective mechanism was favored by higher total metal loadings, possibly due to an increase in the size of metallic aggregates. Alumina supported catalysts present higher ring opening selectivities. The activity for decalin ring opening increased both with metal loading and reaction temperature level.

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.

Optimal Ir/Pt ratio for the ring opening of decalin in zeolite supported catalysts

The aim of this study was to study the ring opening of decalin at 300 and 350°C using Pt–Ir/HY zeolite catalysts. Monometallic Ir(x=1.0, 1.5wt%) and Pt(y=1.0, 1.5wt%) and bimetallic Ir(1.0)Pt(y=0.5, 1.0, 1.5wt%), Ir(1.5)Pt(y=0.5, 1.0, 1.5wt%) catalysts were prepared and catalytically tested. Catalysts were characterized by TPR, pyridine TPD, CO–FTIR, XRD, cyclohexane dehydrogenation and cyclopentane hydrogenolysis activity tests. It was found that the acidic character of Ir oxides species increased the amount of strong acid sites of the support. On the other hand, the Pt content increase favored the formation of medium strength acid sites. The catalysts with higher content of Ir had the higher hydrogenolytic activity while an increase in the Pt content decreased the hydrogenolytic activity. The presence of Pt promoted the dehydrogenation of cyclohexane. Higher yields of dehydrogenated products and increased conversion of cis-decalin were observed at the highest temperature level. The zeolite structure was partially collapsed in the case of the Ir(1.5)Pt(1.5) catalyst. Ir(1.0)Pt(1.0) catalysts at 350°C and Ir(1.5)Pt(1.5) catalysts at 300°C, which showed a good performance, seem to have an adequate balance between metal and acid functions that favors the opening of naphthenic rings.

Catalytic activity of Pt-Re-Pb/Al2O3 naphtha reforming catalysts

BACKGROUND: The main purpose of the naphtha reforming process is to obtain high octane naphtha, aromatic compounds and hydrogen. The catalysts are bifunctional in nature, having both acid and metal sites. The metal function is supplied by metal particles (Pt with other promoters like Re, Ge, Sn, etc.) deposited on the support. The influence of the addition of Pb to Pt-Re/Al2O3 naphtha reforming catalysts was studied in this work. The catalysts were prepared by co-impregnation and they were characterized by means of temperature programmed reduction, thermal programmed desorption of pyridine and several test reactions such as cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n-heptane reforming. RESULTS: It was found that Pb interacts strongly with the (Pt-Re) active phase producing decay in the metal function activity. Hydrogenolysis is more affected than dehydrogenation. Part of the Pb is deposited over the support decreasing the acidity and the strength of the most acidic sites. CONCLUSION: The n-heptane reforming reaction shows that Pb modifies the stability and selectivity of the Pt-Re catalysts. Small Pb additions increase the stability and greatly improve the selectivity to C7 isomers and aromatics while they decrease the formation of low value products such as methane and gases. Copyright © 2011 Society of Chemical Industry

Catalytic performance in selective hydrogenation of citral of bimetallic Pt–Sn catalysts supported on MgAl2O4 and γ-Al2O3

The liquid phase citral hydrogenation, using Pt and PtSn catalysts supported on MgAl2O4 and γ-Al2O3, was studied in a stirred reactor at 70°C and atmospheric pressure. It was found that the addition of Sn to the Pt catalysts increases the selectivity to double unsaturated alcohols for both catalyst series. Besides, monometallic catalysts hydrogenate the α,β-unsaturation with a high selectivity in absence of cyclization secondary products. The performance of these catalysts in the citral hydrogenation was related with the characteristics of the metallic phase. Results from test reactions – cyclohexane dehydrogenation (CHD) and cyclopentane hydrogenolysis (CPH) – H2 chemisorption, 2-propanol dehydration, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS), were used to explain the influence of the support and the Sn loading and postulate the models of the catalytic metallic surface. Results indicated that, a fraction of ionic Sn would be deposited near Pt, thus increasing the polarization of the carbonyl group, and a fraction of metallic Sn could form Pt–Sn alloy phases that would hinder the hydrogenation of the olefinic bonds and would be active to the hydrogenation of the carbonyl group. Both effects contribute to a higher selectivity to unsaturated alcohols in bimetallic PtSn/Al2O3 catalysts than PtSn/MgAl2O4 ones, which display a low alloy formation.

O 2 and O 3 regeneration of PtReSn/Al 2O 3 and PtReGe/Al 2O 3 naphtha reforming catalysts prepared by catalytic reduction

The deactivation and regeneration of naphtha reforming PtReGe/Al 2O 3 and PtReSn/Al 2O 3 catalysts prepared by catalytic reduction were studied. The extent and nature of coke deposition as determined by TPO were related to catalyst properties such as dispersion, acidity and Cl content. The PtReSn catalyst was the most resistant to coke deactivation. Regeneration was performed by calcination in oxygen at 450 °C or ozone at 125 °C at variable regeneration times. Regenerated catalysts were evaluated by cyclopentane hydrogenolysis, cyclohexane dehydrogenation and n-heptane reaction tests. Regeneration by oxygen burning-off was the most effective for decoking. However, oxygen combustion produced more segregation of the metal function than ozone regeneration. With the regeneration conditions used in this work, the original acidity of the catalysts cannot be recovered.

N-Butane dehydrogenation on Pt, PtSn and PtGe supported on γ-Al 2O 3 deposited on spheres of α-Al 2O 3 by washcoating

In this paper the catalytic performance of Pt, PtSn and PtGe catalysts supported on γ-Al 2O 3 (γ-A) prepared by washcoating of spheres of α-Al 2O 3 (α-A) is studied in the n-butane dehydrogenation. For this purpose, the effect of the addition of Sn (0.3 and 0.5 wt.%) and Ge (0.18 and 0.3 wt.%) to Pt (0.3 wt.%) on the activity, selectivity and the catalytic stability was analyzed. The catalyst characterization was carried out by using cyclohexane dehydrogenation (CHD) and cyclopentane hydrogenolysis (CPH) reactions, and also temperature programmed reduction (TPR), H 2 chemisorption, X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM). Results show that important advances in the development of these catalysts were obtained. In this sense the PtSn(0.5)/γ-A/α-A catalyst showed the best catalytic performance (activity, selectivity to all butenes and high stability) in n-butane dehydrogenation reaction. Results showed a different composition of the metallic phase according to the nature of the second metal (Sn or Ge). In fact, PtSn catalysts show a low electronic interaction between the two metals, with a surface segregation of Sn and oxidized Sn stabilized on the support. On the other hand, PtGe catalysts present strong PtGe interactions with probable alloys formation.

Catalytic Properties of Pt−Re/Al2O3Naphtha-Reforming Catalysts Modified by Germanium Introduced by Redox Reaction at Different pH Values

Ge was deposited by catalytic reduction on Pt−Re/Al2O3−Cl base catalysts prepared by coimpregnation. The nominal amounts of Ge incorporated from various impregnation media (H2O, HCl, or NH3) were 0.1, 0.3, 1.0, and 2.0 wt %. The catalysts were characterized by means of the test reactions of cyclohexane dehydrogenation and cyclopentane hydrogenolysis. The catalysts were further characterized by FTIR spectroscopy of adsorbed CO and adsorbed pyridine and by temperature-programmed desorption of pyridine. Blank treatments performed on the Pt−Re/Al2O3 base catalyst in the different media (without Ge addition) showed that the catalytic reduction method modified the properties of the parent catalyst depending on the pH of the solution. The Bronsted acidity decreased as the impregnation pH was increased, whereas the Lewis acidity of the catalyst was not substantially modified by any of the impregnation media. Catalysts with higher Pt−Re interactions were obtained after treatment in a solution of high pH (NH3 mediu...