1-butene Reaction Research Articles

The surface structure of sulfated zirconia: Studies of XPS and thermal analysis

Sulfated zirconias were prepared using two kinds of amorphous zirconia gels, XZO 631 and 632 supplied by MEL Chemicals, and their thermal gravimetrical analyses were carried out. DTG of the former sample showed two peaks based on decomposition of the sulfate species on the surface, the first peak at 680 °C and the second broad one centered at 850 °C. The latter sample indicated only broad peak at 850 °C in the range from 700 to >1000 °C. The first peak for the former sample was ascribed to the decomposition of Zr(SO 4) 2 remained on the surface, and the broad one at 700 to >1000 °C for the both samples was attributed to the catalytically active species. The acidic character of sulfated zirconia calcined at 1000 °C was examined in acid-catalyzed reactions of cumene, ethylbenzene, and butane together with the adsorption heat of Ar, showing a solid acid with acidity higher than that of silica–alumina. It was indicated from the XPS analysis that the S species are composed of SO 4 2−. The results led to a structural model of the active surface to be polysulfate species containing mainly three or four S atoms with two ionic bonds of S O Zr in addition to coordination bonds of S O with Zr, the active site being Lewis sites on the S atoms.

A computational study of alkane hydrogen-exchange reactions on zeolites

In this work, quantum chemical methods were applied to study light alkane hydrogen-exchange reactions on a zeolite cluster, RH + H 3SiOAlH 2(OH′)SiH 3 → RH′ + H 3Si(OH)AlH 2OSiH 3. Methane, ethane, propane, and butane reactions were investigated. The reactants, products, and transition state structures were optimized using the B3LYP density functional theory method and the final energies were calculated using CBS-QB3, a complete basis set composite energy method. The computed activation barriers ranged from 28.32 kcal/mol for secondary hydrogen exchange of butane to 33.53 kcal/mol for methane. The relationship between activation energy and deprotonation energy was also investigated and a linear correlation was proposed in this work.

A DFT study on the double bond migration of butene catalyzed by ionic pair of 1-ethyl-3-methyl-imidazolium fluoride

The double bond migration of butene catalyzed by 1-ethyl-3-methyl-imidazolium fluoride (EmimF) has been studied using quantum chemical method. The geometries of reactant, transition state and product for the isomerization have been optimized by density functional theory (DFT) at the B3PW91/6-31G(d,p), 6-311++G(d,p) and aug-cc-PVDZ levels. The computed results show that the 4-H atom on imidazole ring of EmimF has a good catalytic activity to the double bond migration of butene and the catalytic reaction of 1-butene to 2-butene is a synergetic and elementary process. The apparent activation energy of isomerization is about 197 kJ/mol.

Quantum chemical and conventional TST calculations of rate constants for the OH+alkane reaction

Abstract Reactions of OH with methane, ethane, propane, i -butane, and n -butane have been modeled using ab initio (MP2) and hybrid DFT (BHandHLYP) methods, and the 6-311G(d,p) basis set. Furthermore, single-point calculations at the CCSD(T) level were carried out at the optimized geometries. The rate constants have been calculated using the conventional transition-state theory (CTST). Arrhenius equations are proposed in the temperature range of 250–650 K. Hindered Internal Rotation partition functions calculations were explicitly carried out and included in the total partition functions. These corrections showed to be relevant in the determination of the pre-exponential parameters, although not so important as in the NO 3 + alkane reactions [G. Bravo-Perez, J.R. Alvarez-Idaboy, A. Cruz-Torres, M.E. Ruiz, J. Phys. Chem. A 106 (2002) 4645]. The explicit participation of the tunnel effect has been taken into account. The calculated rate coefficients provide a very good agreement with the experimental data. The best agreement for the overall alkane + OH reactions seemed to occur when the BHandHLYP geometries and partition functions are used. For propane and i -butane, in addition to the respective secondary and tertiary H-abstraction channels, the primary one has been considered. These pathways are confirmed to be significant in spite of the large differences in activation energies between primary and secondary or primary and tertiary channels, respectively of propane and i -butane reactions and should not be disregarded.

One-step preparation of manganese-, iron-, and aluminum-promoted sulfated zirconias for reaction of butane to isobutane

Highly active superacids of Mn-, Fe-, and Al-sulfated ZrO2's for the isomerization of butane to isobutane were obtained by exposing zirconia gel to aqueous solutions of 0.05 M MnSO4, 0.25 M FeSO4, and 0.5 M Al2(SO4)3 followed by calcining in air at 700, 600, and 675°C, respectively. The catalysts were much more active than the superacid of sulfated zirconia, the temperature difference to show the same conversion (20%) between the catalysts and sulfated zirconia being 85, 77, and 85°C for the Mn-, Fe-, and Al-catalysts, respectively.

Investigation of the morphology and the active site distribution of Rh-graphimet

In order to gain information on the location and on the morphology of the metal content of Rh-graphimet, structural investigations were performed before and after medium-temperature reduction (MTR, 573 K, 1 h), by means of X-ray photoelectron spectroscopy, transmission electron microscopy, BET surface analysis, small-angle X-ray scattering and H 2 titration. The active site distributions of the samples were characterized by 1-butene titration. It was established that the metal content of Rh-graphimet was situated in part in the interlayer space and in part on the surface of the graphite as finely-dispersed Rh crystallites. After MTR, the morphology of the surface Rh particles was retained and no significant differences in the structural parameters were observed. Nevertheless, the number of active sites in Rh-graphimet strongly depended on the temperatures of both pretreatment and the catalytic reaction. The main reactions of 1-butene for the pristine sample were cis- and trans-isomerization. Deactivation at 323 K affected the hydrogenation sites rather than the isomerization centres. For the catalytic activity of Rh-graphimet, the smallest Rh clusters of 1 nm were found to be of crucial importance and the loss of activity observed on MTR was correlated with the effect of sintering and encapsulation of Rh particles in the graphite host.

Shape-selective catalysts: quasi-two-dimensional Pd-particles encapsulated in graphite

Pd–graphites were prepared by reduction of PdCl 2–graphite intercalation compounds (PdCl 2–GICs). Transmission electron microscope (TEM) measurements on the samples indicated that Pd nanoparticles with a wide size distribution were formed, mostly encapsulated inside the graphite host. The quasi-two-dimensional character of the Pd nanoparticles was confirmed by H 2 sorption studies, which revealed the absence of β-hydride formation over a broad range of pressure. Although the structures of the three Pd–graphites studied were very similar, differences were found between them in terms of their catalytic performance in the gas-phase reactions of 1-butene, cis-2-pentene and cyclohexene. It was established that the transformations of both 1-butene and cis-2-pentene took place in the interlamellar space of the graphite, whereas, in consequence of the the non-planar character of the substrate, the diffusion of cyclohexene between the graphite layers was sterically hindered. This molecular sieving effect implies that the Pd–graphites may be regarded as shape-selective catalysts. Pretreatment at 473 K was found to lower the catalytic activities considerably. The experimental evidence indicated that restructuring of the Pd crystallites resulted in a moderate aggregation of the active Pd-particles available for the reactant molecules.

Solid-state NMR studies of n-butene isomerisation over H-ferrierite

The reaction of 1-butene over ferrierite has been studied by 13C MAS NMR. It is shown that extensive double bond isomerisation and the formation of dimers, mainly dimethyl-hexenes and trimethyl-pentenes, dominate the early catalytic events. Strong interactions between the butene double bond and the Brönsted acid sites shift and broaden the butene olefinic signal extensively. The olefinic carbon signals of isobutene and butene dimers are not observed in these experiments because of the interactions mentioned above and the effect of carbon scrambling. At higher reaction temperatures, the formation of isobutene dominates the spectra and this catalytic event parallels the consumption of 3,4,4-trimethyl-2-pentene. It is suggested that that 3,4,4-trimethyl-1-pentene isomerises to 2,4,4-trimethyl-1-pentene which in turn, rapidly cracks to form isobutene. At higher reaction temperatures, isobutene undergoes extensive secondary reaction leading to C 1–C 5 paraffins and aromatic coke.

Low-Temperature Isomerization of 1-Butene on Mo2N/γ-Al2O3 Catalyst Studied by in Situ FT-IR Spectroscopy

The adsorption and reaction of 1-butene on Mo2N/γ-Al2O3 catalyst have been studied by in situ FT-IR spectroscopy at low temperatures, 145 K to room temperature (RT). The adsorbed 1-butene can be converted to cis- and trans-2-butenes below 201 K on Mo2N/γ-Al2O3 catalyst. The result of coadsorption of 1-butene with CO indicates that 1-butene is mainly adsorbed on the surface Mo sites of the nitrided catalyst. No isomerization of adsorbed 1-butene and 2-butenes on reduced passivated Mo2N/γ-Al2O3 sample below RT is observed. It is suggested that the double-bond migration (DBM) of 1-butene is mainly proceeded via an alkyl species on the surface cus Mo sites of Mo2N/γ-Al2O3 catalyst. This resembles the behaviors of Group VIII metals in the isomerization of butenes. The incorporated nitrogen atoms are proposed to devote to both the valence state of surface Mo sites and the interaction between 1-butene and the nitrided catalyst. A possible path from 1-butene conversion to 2-butenes on Mo2N/γ-Al2O3 catalyst is proposed.

In situ FT-IR study on the reaction path of skeletal isomerization of n-butene over different zeolites

Adsorption and reaction of 1-butene, cis- and trans-2-butene and isobutene on H-ZSM-5 and H-FER were studied by FT-IR spectroscopy between 30–450°C. n-Butenes were monomolecularly adsorbed via π-bonding on H-FER at 30°C. At elevated temperatures butadiene was monitored on H-FER, which was then transformed into dialkyldiphenyl. On H-ZSM-5 all butene isomers were adsorbed via π-bonds, followed by dimerization. From these results and from catalytic measurements a monomolecular pathway is proposed on H-FER and a bimolecular one on H-ZSM-5.

Characterization and catalytic activity of Ni–Al and Zn–Cr mixed oxides obtained from layered double hydroxides

In this work, the preparation of Ni–Al and Zn–Cr layered double hydroxides (LDHs) and their transformations upon calcination are described. The LDHs were prepared from their nitrate salts by pH controlled precipitation. They were characterized before and after calcination by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and BET surface area measurements. The acid–base properties of the dehydrated materials were also investigated by temperature programmed CO2 desorption and the double-bond isomerization reaction of 1-butene. It was found that upon calcination mixed oxides with large surface areas were formed, which possessed mainly acidic sites of moderate strength.

Effects of site isolation on n-butenes catalytic oxidation and isomerization over bismuth molybdates

The behaviour of the oxidative dehydrogenation and isomerization reactions of 1-butene, cis-2-butene and trans-2-butene in the presence of oxygen over bismuth molybdates is studied. The significant observed differences are interpretable in the light of the site isolation concept, taking into account the pronounced different reduction power of the tested olefins. Important aspects of the mechanisms of the involved reactions are discussed.

Reaction of butane to isobutane on silica-supported 12-tungstosilicic acid

The heteropolyacids 12-tungstosilicic acid (TSA), 12-tungstophosphoric acid (TPA), 12-molybdosilicic acid (MSA) and 12-molybdophosphoric acid (MPA) were supported on SiO2 and examined in the gas–solid phase reaction of butane to isobutane. Use of a support was effective for TSA and TPA whereas no reaction was observed with MSA or MPA. Effectiveness of the support for TSA was observed with ZrO2 and Al2O3 but not with TiO2, SnO2, or Fe2O3. The most active catalyst was prepared by impregnating SiO2 with an aqueous solution of 40 wt% TSA followed by water evaporation and heat-treating in air at 300 °C (40% TSA/SiO2). The catalytic activity was more than doubled when a physical mixture of 40% TSA/SiO2 and Pt/ZrO2 was used.

A Magnetically Ordered Non-Stoichiometric Zinc Ferrite for the Oxidative Dehydrogenation Reactions.

ABSTRACTZnFe2O4nanoparticles were prepared by hydrothermal reduction approach. A considerable amount of α-Fe2O3was segregated in the as-synthesized sample, which diffused into the tetrahedral and octahedral sites of the ZnFe2O4spinel structure with increasing the annealing temperature. The introduction of Fe3+into the tetrahedral positions was observed by Mössbauer spectra. Magnetization measurements showed an unusual ferrimagnetic behavior of the ZnFe2O4phase, even at room temperature, confirming the introduction of Fe3+into the tetrahedral sites of the spinel structure. Catalytic activity measured in the oxidative dehydrogenation of 1-butene reaction increased with increasing annealing temperature, indicating that those interactions of Fe3+in tetrahedral and octahedral positions also promotes the activity and selectivity to butadiene formation.

FT-IR Study of the Isomerization of n-Butene over Different Zeolites

Adsorption and reaction of 1-butene, cis- and trans-2-butene, and isobutene on silicalite H-ZSM-5 and H-FER were studied by FT-IR spectroscopy. On silicalite the different butenes were only physisorbed and no interaction took place. Over H-ZSM-5, hydrogen-bonded cis- and trans-2-butenes were initially formed followed by dimerization. Over H-FER the adsorbed 1-butene was converted into cis- and trans-2-butenes which were hydrogen-bonded to the acidic OH-groups of the zeolite and no further dimerization was found. Since the Bronsted acidity of H-FER and H-ZSM-5 is comparable it can be concluded that the pore size and pore structure and not the acidity plays the important role for the observed behavior. From this study and literature results, a monomolecular mechanism is proposed for the isomerization of n-butenes to isobutene over both types of zeolites (H-ZSM-5 and H-FER).

Tungsten catalysts supported on activated carbon: II. Skeletal isomerization of 1-butene

Tungsten catalysts supported on activated carbon were used in the isomerization reaction of 1-butene. The results obtained were compared with thoseof other tungsten catalysts supported on Al 2 O 3 , SiO 2 , and TiO 2 . When the catalysts supported on activated carbon were pretreated in He flow, at either 623 or 748 K, the activity to produce isobutene increased linearly with the surface acidity of the catalysts, and the specific activity after pretreatment at 623 K was higher than that after pretreatment 748 K. The activity to produce isobutene did not decrease with reaction time and no dimerization by-products were obtained. After the pretreatments at 973 and 1223 K, there was a loss of activity with reaction time,and by-products from the dimerization of butenes appeared. The presence of water vapor in the reaction mixture was also studied. The catalysts supported on Al 2 O 3 , SiO 2 , and TiO 2 and pretreated under the same conditions, at both 623 and 748 K, showed a decrease in activity to produce isobutene with reaction time and the catalyst supported on Al 2 O 3 was the most active. Results show the importance of the support in these kinds of catalysts and seem to indicate that the activated carbon, due to its surface basicity, moderates the surface acidity of the tungsten oxide particles. Therefore, with a lower surface acidity of the catalyst it has an activity similar to that found with the Al 2 O 3 -W catalysts but without deactivation.

Reactions of Tantalum Oxide Cluster Cations with 1-Butene, 1,3-Butadiene, and Benzene

Branching ratios for the reactions of 1-butene, 1,3-butadiene, and benzene with stoichiometric tantalum oxide clusters (TaO2-3+, Ta2O4-5+, and Ta3O7-8+) are reported. The major reaction product for most of the clusters is cracking of the C2−C3 bond of 1-butene and 1,3-butadiene to produce TaxOyC2H4+. Additionally, Ta2O4+ was the most reactive cluster toward cracking the C2−C3 bond of both 1-butene and 1,3-butadiene. For a majority of these clusters there were additional cracking channels to produce TaxOyCH3+ and TaxOyC3Hz+, where z = 5−6, which occur under multiple collision conditions for 1-butene and 1,3-butadiene. Under multiple collision conditions, TaO2+, Ta2O4+, and Ta3O7+ exhibited the reaction channels of TaxOyC5H9+ and TaxOyC6H10+ when reacted with 1-butene. In reactions with 1,3-butadiene, secondary reaction channels of TaxOyC5H7+ and TaxOyC6H8+ were also observed for TaO2+, Ta2O4-5+, and Ta3O7+. Additionally, under multiple collision conditions, TaO2+ and Ta2O4+ also displayed reaction channels of TaxOyC7H9+ and TaxOyC8H10+. Reactions of most of the stoichiometric tantalum oxide clusters with benzene showed a cracking channel forming TaxOyC4H4+ and a dehydration channel to form TaxOy-1C6H4+. The most reactive cluster toward cracking benzene was Ta3O8+, and the most reactive cluster toward the dehydration reaction was TaO2+. Reactions of the aforementioned unsaturated hydrocarbons with oxygen-rich clusters (TaO4-5+, Ta2O6-7+, and Ta3O9-10+) are also reported. The major reaction channel of most of these clusters involves loss of molecular oxygen to form the smaller, more stable stoichiometric clusters, which then proceed to react with or associate the hydrocarbon gas.

Aromatization of butane on Pt–Ge intermetallic compounds supported on HZSM-5

Catalytic properties of Pt–Ge intermetallic compounds supported on HZSM-5 zeolites were studied in the conversion of butane into aromatic hydrocarbons under atmospheric pressure at 823 K. Pt–Ge intermetallic compounds were prepared on HZSM-5 by chemical vapor deposition of Ge(acac) 2Cl 2 on Pt-loaded HZSM-5 followed by the treatment with hydrogen at 823 K. XRD revealed the transformation of Pt particles into the intermetallic phases, Pt 2Ge, Pt 3Ge 2, PtGe, Pt 2Ge 3 and PtGe 2, during the CVD and subsequent hydrogen treatment. In the reaction of butane, Pt–Ge intermetallic compounds supported on HZSM-5 exhibited higher selectivity to aromatic hydrocarbons than HZSM-5 and Pt-loaded HZSM-5. This would be caused by the high activity for the dehydrogenation of butane and alkylcyclohexene compared with HZSM-5 and the low activity for the hydrogenolysis and hydrogenation to form methane and ethane compared with Pt-loaded HZSM-5. Pt–Ge intermetallic compounds with Pt/Ge molar ratio of 1.0 supported on HZSM-5 showed the highest selectivity to aromatic hydrocarbons (57 C%). PtGe was suggested to be the most effective for the formation of aromatic hydrocarbons from butane among the Pt–Ge intermetallic compounds.

IR Study of Double Bond Migration of 1-Butene on SiO2-Al2O3.

Adsorption and reaction of 1-butene on silica-alumina (SA) were studied by FT-IR at below room temperature. Two types of adsorption sites for 1-butene were identified by different C=C stretching frequencies, 1633cm-1 on Bronsted acid sites and 1607cm-1 on Lewis acid sites. On fully hydroxylated SA without Lewis acid sites, the reaction from 1-butene to the mixture of cis-2-butene and trans-2-butene was observed at 246K only in the presence of gaseous molecules. On the other hand, when Lewis acid sites existed, the same reaction took place even at 221K in evacuation (reaction of irreversibly adsorbed species). Lewis acid sites were confirmed to be occupied first by some kinds of hydrocarbon species that would catalyze the reaction. The present observation supports the mechanism on SA previously proposed, and the observation also distinguishes the difference in mechanism on SA from that on zeolites.

Catalysis of Ruthenium-Metal Oxides Mechanically Mixed with Sulfated Zirconia for Reaction of Butane to Isobutane

A highly active catalyst for the skeletal isomerization of butane to isobutane was obtained by mechanically mixing SO4/ZrO2 and Ru/SnO2; Ru/SO2 was prepared by impregnating tin hydroxide with a solution of RuCl3 followed by calcining at 450°C (0.5 wt.% Ru). The catalyst was much more active than Ru-SO4/ZrO2 prepared by co-impregnation of zirconia with the Ru and sulfate materials the temperature difference to show the same conversion between both catalysts being 57°C. The effect of mixing of Ru was observed with other metal oxides as supports, Fe2O3, Al2O3, ZrO2, TiO2, and SiO2; the calcination temperature of the Ru-impregnated hydroxides was 250, 300, and 400°C for the latter three, respectively.