Catalysts For Selective Ring Opening Research Articles

Elucidating the Morphology Effect of Pt Nanocrystals on Pt/CNT-USY Catalysts for Selective Ring Opening of Decalin

Elucidating the Morphology Effect of Pt Nanocrystals on Pt/CNT-USY Catalysts for Selective Ring Opening of Decalin

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.

Transition metal sulfides on zeolite catalysts for selective ring opening

Bifunctional catalysis combining acidic catalysts and sulfide active phases is usually related to hydrocracking catalysts which balances the hydrogenation function of a NiMo (NiW) alumina supported sulfide catalysts and the acidic function of a zeolite. The discovery of sulfur-resistant catalysts for selective ring opening (SRO) is an important challenge for refiners, considering the future legislation on cetane index of diesel fuels. In the present work, we studied the properties of various transition metal sulfides (TMS) supported on Y zeolite in gas-phase decalin hydroconversion at high hydrogen pressure (5 MPa) in the presence of 0.8 % H2S concentration. This screening shows high activities for noble metal based sulfides with a mechanism which proceeds by skeletal isomerization induced by the zeolite. Catalytic activity was improved by the use of ternary sulfides such as Ni1-xRuxS2 or NiRh2S4 on Y zeolites. High decalin conversion levels can be reached below 250 °C with more of 20 % of ring opening products and thanks to the use of comprehensive GC, a detailed mechanism of the SRO of decalin is given.

Selective Ring Opening of Ethylbenzene on Bifunctional Catalyst Pt–Ir over Hierarchical USY Zeolite

A bifunctional catalyst for selective ring opening (SRO) has been designed using a hierarchical zeolite as support. This material was prepared introducing additional mesoporosity in the microporous structure of a USY zeolite, by surfactant-templating post-synthetic mesostructuring process. Monometallic and bimetallic Pt(x)−Ir(y) catalysts with different metal loadings and Pt/Ir mole ratio have been prepared. In addition, to optimise the acid-metal balance, the acidity of the support has been modulated via ion-exchange process with Na+. The catalytic behaviour of the prepared materials has been evaluated with ethylbenzene hydrogenation and SRO simultaneous reaction in a continuous-flow fixed-bed reactor, at 275°C and 3 MPa. Pt(2)−Ir(1) resulted the most promising metallic combination. The high hydrogenolytic activity of Ir, along with the high hydrogenation activity and cracking limitation of Pt attained a high paraffins production. This behaviour was improved modulating the acidity of the support. Thus, Pt(2)−Ir(1)/Na−FAU−CTAB catalyst maximized the yield to paraffins which improve the cetane number of fuels.

Selective ring opening of decalin over bifunctional RuS2/zeolite catalysts

The discovery of sulfur-resistant catalysts for selective ring opening (SRO) is an important challenge for refiners, considering the future legislation on cetane index of diesel fuels. In the present work, we studied the properties of RuS2 supported on several zeolites in gas-phase decalin hydroconversion at high hydrogen pressure (5 MPa) in the presence of 0.8% H2S concentration. Catalytic bifunctionality was investigated by changing the Ru loading or support acidity. The addition of RuS2 strongly improved catalytic activity of an HY zeolite, decreased coke deposition and dehydrogenation and increased selectivity towards RO products. The mechanism mainly proceeds from skeletal isomerization induced by the acidity of the zeolite but the hydrogen activation properties of RuS2 are beneficial to the activity and stability of the catalyst.

Tactical control of Ni-loading over W-supported Beta zeolite catalyst for selective ring opening of 1-methylnaphthalene

Due to the need for better methods to upgrade heavy oil, selective ring opening (SRO) of multi-ring aromatics to mono-aromatics has attracted great interest. The SRO reaction can be done by hydrogenation and hydrocracking, catalyzed by the metallic (from metal element) and acidic (from zeolite) functions of bifunctional catalysts. We investigated the effect of wet-impregnated Ni and W metals over Beta zeolite on the characteristics of metal and acid sites, and found the correlation with their catalytic performance for the SRO reaction of 1-methylnaphthalene as a representative multi-ring aromatics. Primarily, W metal species was estimated to be more active than Ni metal species for the SRO reaction. Based on fundamental insight into these bifunctional catalysts, we described a facile approach to enhance the yield of the SRO reaction employing NiW-loaded Beta zeolite catalysts with various Ni contents. The balance of the metallic and acidic functions was modified by variation of the Ni content, and gradually shifted the product distribution showing a close relationship between the SRO performance and Ni content. We expect that this study can provide a logical perspective for designing selective bifunctional catalysts based on a better understanding of the interaction between metal and zeolite characteristics.

Influence of rhodium content on the behavior of Rh/SiO2–Al2O3 catalysts for selective ring opening of decalin

Decalin ring-opening is favored on Rh/SiO2–Al2O3 bifunctional catalyst with an optimized acid/metal balance.

Bifunctional MCM-41 aluminosilicate supported Ir with adjusted metal and acid functionality for catalytic ring opening of 1,2-dimethylcyclohexane

Herein we report H-AlMCM-41 aluminosilica supported Ir materials with adjusted acid/metal function as bifunctional catalysts for selective ring opening (RO) of 1,2-dimethylcyclohexane (1,2-DMCH) at 330°C and 3MPa to primary ring opening products (P-ROP), which are defined as C8 alkanes. Large-pore H-AlMCM-41 materials were synthesized with Si/Al atomic ratios of 20 and 45 and impregnated for the first time with 0.6–1.8wt% Ir to afford xIr/H-Al-MCM-41(y) bifunctional catalysts (x=Ir content in wt%, y=Si/Al ratio) with moderate Brønsted acidity and relatively strong hydrogenolysis tendency. The optimum catalytic performance was achieved with 1.2Ir/H-AlMCM-41(45), which gave 31% yield of desired alkane products at 71% conversion of 1,2-DMCH. In contrast, zeolite based 0.5Ir/H-Beta-25 as well as the purely metallic 0.7Ir/Na-AlMCM-41(20) catalysts did not exhibit suitable catalytic performance for the production of C8 alkanes compared to Ir/H-AlMCM-41 catalysts. All materials were thoroughly characterized by N2 adsorption, solid-state NMR, TEM and FTIR of adsorbed pyridine, and their catalytic behavior was discussed in light of their physiochemical properties.

The Effect of K and Acidity of NiW-Loaded HY Zeolite Catalyst for Selective Ring Opening of 1-Methylnaphthalene.

Bi-functional catalysts were prepared using HY zeolites with various SiO2/Al2O3 ratios for acidic function, NiW for metallic function, and K for acidity control. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction was investigated using the prepared bi-functional catalysts with different levels of acidity in a fixed bed reactor system. In NiW/HY catalysts without K addition, the acidity decreased with the SiO2/Al2O3 mole ratio of the HY zeolite. Ni1.1W1.1/HY(12) catalyst showed the highest acidity but slightly lower yields for the selective ring opening than Ni1.1W1.1/HY(30) catalyst. The acidity of the catalyst seemed to play an important role as the active site for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. Catalyst acidity could be controlled between Ni1.1W1.1/HY(12) and Ni1.1W1.1/HY(30) by adding a moderate amount of K to Ni1.1W1.1/HY(12) catalyst. K0.3Ni1.1W1.1/HY(12) catalyst should have the optimum acidity for the selective ring opening. The addition of a moderate amount of K to the NiW/HY catalyst must improve the catalytic performance due to the optimization of catalyst acidity.

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.

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.

Y(NO 3) 3·6H 2O catalyzed regioselective ring opening of epoxides with aliphatic, aromatic, and heteroaromatic amines

Yttrium nitrate hexahydrate [Y(NO 3) 3·6H 2O] was found to be an efficient catalyst for selective ring opening of epoxides with aliphatic, aromatic, and heteroaromatic amines at room temperature under solvent-free conditions. The system tolerated a variety of hindered and functionalized epoxides/amines and afforded the desired β-amino alcohols at low catalyst concentration.

Mechanistic Implications of Ring-Opening Rate vs Hydrogen Pressure Functions

Bitumen-derived crude and heavy oils require severe processing and produce middle distillate product with poor ignition quality. This becomes a concern to refiners as tighter specifications on transportation fuel are promulgated. One process to address this issue is selective ring opening of cycloparaffins to reduce the number of ring structures, while retaining the carbon number of a product molecule. The process involves bifunctional catalysts, both metal and acid sites, working in high-pressure, high-temperature reactor systems in the presence of hydrogen. The acidic sites catalyze dehydrogenation, cracking, isomerization and dealkylation, while the metal sites promote hydrogenation, hydrogenolysis and isomerization. Various compounds containing single, double and multiple rings have been used to model the ring-opening reactions and a number of mechanisms have been proposed. The five-membered ring readily undergoes ring-opening reaction on either acid or metal catalysts with the selectivity and activity dependent on the nature of the supported metal catalyst. The ring opening of six-membered ring compounds is secondary, requiring an acidic function to isomerize a six-membered ring cycloparaffin to a five-membered ring. A balanced metallic-acidic function catalyst is necessary to achieve optimal performance. A system dominated by acid function results in excess cracking, while a catalytic system with high concentration of metals leads to mainly hydrogenation. Commercial hydrocracking catalysts using transition metal sulfides on acidic supports usually require severe operating conditions due to their low activities of the metal sulfide compared to metal sites, leading to extensive cracking of cycloparaffin side chains. Noble metals supported on acidic oxides are the most active catalysts for selective ring opening, but these catalysts are very sensitive to poisoning by sulfur compounds in petroleum feedstocks. An understanding of the chemistry of selective ring-opening catalysts, combined with theoretical studies of structure–activity relationships and high throughput experimentation methods, provides opportunities in searching for new generations of selective ring-opening catalysts with high-performance and sulfur resistance.

Hydrogen Pressure Dependence in the Ring-Opening Reactions of Substituted Cyclobutanes over Rh/SiO2Catalyst at Various Temperatures

Bitumen-derived crude and heavy oils require severe processing and produce middle distillate product with poor ignition quality. This becomes a concern to refiners as tighter specifications on transportation fuel are promulgated. One process to address this issue is selective ring opening of cycloparaffins to reduce the number of ring structures, while retaining the carbon number of a product molecule. The process involves bifunctional catalysts, both metal and acid sites, working in high-pressure, high-temperature reactor systems in the presence of hydrogen. The acidic sites catalyze dehydrogenation, cracking, isomerization and dealkylation, while the metal sites promote hydrogenation, hydrogenolysis and isomerization. Various compounds containing single, double and multiple rings have been used to model the ring-opening reactions and a number of mechanisms have been proposed. The five-membered ring readily undergoes ring-opening reaction on either acid or metal catalysts with the selectivity and activity dependent on the nature of the supported metal catalyst. The ring opening of six-membered ring compounds is secondary, requiring an acidic function to isomerize a six-membered ring cycloparaffin to a five-membered ring. A balanced metallic-acidic function catalyst is necessary to achieve optimal performance. A system dominated by acid function results in excess cracking, while a catalytic system with high concentration of metals leads to mainly hydrogenation. Commercial hydrocracking catalysts using transition metal sulfides on acidic supports usually require severe operating conditions due to their low activities of the metal sulfide compared to metal sites, leading to extensive cracking of cycloparaffin side chains. Noble metals supported on acidic oxides are the most active catalysts for selective ring opening, but these catalysts are very sensitive to poisoning by sulfur compounds in petroleum feedstocks. An understanding of the chemistry of selective ring-opening catalysts, combined with theoretical studies of structure–activity relationships and high throughput experimentation methods, provides opportunities in searching for new generations of selective ring-opening catalysts with high-performance and sulfur resistance.