DOI: 10.1002/cctc.201200414

Selective Hydrogenation of 1,3-Butadiene and 1-Butyneover a Rh/Chitosan Catalyst Investigated by usingParahydrogen-Induced PolarizationDanila A. Barskiy,[a, b] Kirill V. Kovtunov,*[a, b] Ana Primo,[c] Avelino Corma,[c] Robert Kaptein,[b, d]

and Igor V. Koptyug[a, b]

Introduction

Chitosan is a naturally abundant and renewable polymer withexcellent properties such as biodegradability, biocompatibility,and nontoxicity.[1, 2] Strong affinity of this biopolymer for metalions, owing to the presence of free amino groups, as well asits high sorption capacities for catalytic metals such as copper,platinum, palladium, gold, and rhodium, makes chitosan a pro-spective material for many fields of modern chemical indus-try.[1–6] These properties of chitosan explain the increasingnumber of papers dedicated to the study of its use as a sup-port for catalytic chemical reactions.[1–12] Chitosan-supportedmaterials can catalyze oxidation, polymerization, carbonylationreactions, synthesis of fine chemicals, and hydrogenation.[7–11]

Therefore, chitosan-based catalysts represent an interestingand important area of research. Among metals indicating affin-ity for complex formation with chitosan, rhodium demon-strates high activity in the hydrogenation reactions of unsatu-rated compounds.[9]

Selectivity toward the formation of a desired product is oneof the most important characteristics of any catalytic processalong with the requirements of high activity and stability. Theselective hydrogenation of alkynes and dienes in gaseousstreams rich in C2, C3, and C4 alkenes is a major problem in pet-rochemical industry.[13, 14] Steam and catalytic cracking of hydro-carbons lead to the formation of minor amounts of alkynesand/or dienes, which have to be selectively removed from thefeed before alkenes can be used in polymerization or selectiveoxidation to avoid catalyst poisoning. Therefore, producinghigh-purity butenes for polymerization and copolymerizationdemands selective hydrogenation of byproducts (1,3-buta-diene and butynes) present in butene streams. Because the de-sired product is an alkene, the catalyst should not hydrogenateany amount of butene, and butadiene/butyne should be pref-

erentially converted to butene rather than to butane. Remem-ber that small quantities of dienes and alkynes are hydrogenat-ed in the presence of a large excess of butene, and theirdegree of conversion to butane has to be as low as possibleeven if they are completely removed.[15] Thus, selective hydro-genation requires a detailed understanding of the reactionmechanism and the processes occurring on the catalystsurface.

In the last few years, parahydrogen-induced polarization(PHIP) has emerged as a technique for investigating hydroge-nation reactions in heterogeneous catalysis.[16–18] For PHIP ef-fects to be observed, a catalyst should be able to transfer bothhydrogen atoms of a single parahydrogen molecule to thesame product molecule. Such a pairwise hydrogen additionmechanism ensures that the original correlation of the nuclearspins of the two hydrogen atoms of a parahydrogen moleculeis converted to the polarization of these two hydrogen atoms

Hydrogenation of 1,3-butadiene and 1-butyne over the Rh/chi-tosan catalyst in gaseous and liquid phases was investigatedby using the NMR and parahydrogen-induced polarizationtechnique. The Rh/chitosan system was a very selective catalystfor the partial hydrogenation of 1,3-butadiene and 1-butyne to1- and 2-butenes. The catalyst demonstrated high activity inthe hydrogenation of 1-butyne after its activation in the hydro-genation of 1,3-butadiene. Therefore, the Rh/chitosan catalystwas used for the catalytic removal of 1,3-butadiene and 1-

butyne from gaseous butene streams. Moreover, the syn- andanti-addition of the hydrogen molecule to substrates proceed-ed in a pairwise manner in the gas phase heterogeneous hy-drogenation as was demonstrated by parahydrogen-inducedpolarization. However, in the liquid phase hydrogenation of 1-butyne, both hydrogen atoms from the same hydrogen mole-cule were added to 1-butyne only through the syn-additionroute.

[a] D. A. Barskiy, Dr. K. V. Kovtunov, Prof. I. V. KoptyugLaboratory of Magnetic Resonance MicroimagingInternational Tomography Center SB RASInsitutskaya Street, 3 A, 630090 Novosibirsk (Russia)Fax: (+ 7) 383-3331399E-mail : kovtunov@tomo.nsc.ru

[b] D. A. Barskiy, Dr. K. V. Kovtunov, Prof. R. Kaptein, Prof. I. V. KoptyugNovosibirsk State UniversityPirogova Street, 2, 630090 Novosibirsk (Russia)

[c] Dr. A. Primo, Prof. A. CormaInstituto de Tecnologia Quimica UPV-CSICAvda. de los Naranjos, s/n, 46022 Valencia (Spain)

[d] Prof. R. KapteinBijvoet CenterUniversity of UtrechtPadualaan 8, 3584 CH Utrecht (The Netherlands)

ChemCatChem 2012, 4, 1 – 6 � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1

These are not the final page numbers! ��

once they are in the reaction product.[19] This is observed asa strong enhancement of the corresponding signals in the1H NMR spectra, which can be as high as 104–105 in the mag-netic fields of modern high-resolution NMR spectrometers.[20]

Such a strong signal enhancement produced by PHIP allowsone to observe even minor products of a reaction and, in cer-tain cases, to detect reaction intermediates.[21] Tracking the po-sitions of these “PHIP-labeled” hydrogen atoms in the productsof hydrogenation reactions makes it possible to explore reac-tion mechanisms.[16] The fact that supported metal heterogene-ous catalysts demonstrate PHIP effects confirms that the pair-wise addition of hydrogen to unsaturated compounds contrib-utes to the reaction to some extent even if the reaction occursat the surface of a metal particle, and the dissociation of hy-drogen on the metal surface with the subsequent addition ofrandom hydrogen atoms to a substrate is expected to domi-nate.[16, 18] Supported rhodium catalysts produce stronger PHIPeffects in gas and liquid phase hydrogenations of unsaturatedhydrocarbons[22] compared to some other noble metals. There-fore, rhodium-containing heterogeneous catalysts in combina-tion with chitosan are of potential interest as efficient sourcesof PHIP. The PHIP technique has already been demonstrated tobe a very efficient tool for the in situ visualization of catalyticreactors in conventional and remote-detected magnetic reso-nance imaging.[23]

Results and Discussion

1,3-Butadiene hydrogenation

Herein, we used rhodium supported on preformed hydrogelpolymers of chitosan microspheres. The presence of aminogroups in chitosan together with mild metal reduction and su-percritical CO2 drying allows us to achieve a high rhodiummetal dispersion in the Rh/chitosan aerogel. A representativeTEM image of the Rh/chitosan catalyst is presented in Figure 1.The histogram of the metal particles indicates that most of thecrystallites are in between 2 and 3 nm, and some particles are1 nm in size or smaller. Such a high metal dispersion shouldproduce an active hydrogenation catalyst. Thus, we have usedthe new Rh/chitosan catalyst in the gas phase selective hydro-genation of 1,3-butadiene and 1-butyne.

A first attempt to hydrogenate 1,3-butadiene with parahy-drogen over the Rh/chitosan catalyst at room temperature pro-duced no noticeable amounts of any product. Increasing thetemperature to 50 8C resulted in the detection of a smallamount of products. After the temperature was increased to100 8C, significant amounts of butene were detected and in-tensive polarization patterns were observed for hydrogenationproducts in the 1H NMR spectra. Because the hydrogenation of1,3-butadiene was performed in the strong magnetic field (7 T)of an NMR magnet, a PASADENA polarization pattern was ex-pected,[20a] which usually appears as enhanced antiphase mul-tiplets in the 1H NMR spectra. Strong PHIP effects were ob-served for both 1- and 2-butenes (Figure 2 b). The distinctivefeature of the Rh/chitosan catalyst is that this catalyst is highlyselective in semihydrogenation while the yield of butane is

quite low. The first stage of 1,3-butadiene hydrogenation isclearly the addition of hydrogen to one double bond of 1,3-butadiene, which produces an intense polarization for CH2 andCH3 groups of 1-butene (labeled as 5 and 6, respectively) ifparahydrogen is used in the reaction.

Hydrogenation with normal hydrogen (Figure 2 a) makes itpossible to calculate conversion values for the hydrogenationreaction. The gaseous mixture after the reaction contained44 % of unreacted 1,3-butadiene, 29 % of 1-butene, 26 % of 2-

Figure 1. a) TEM image of the Rh/chitosan catalyst. Inset : Statistical study ofthe rhodium nanoparticle size. b) High-resolution TEM image of rhodiumnanoparticles showing four nanoparticles of size around 2 nm. c) High-reso-lution TEM image of one nanoparticle showing the crystal lattice and theround shape of the nanoparticle. d) Selected-area electron diffraction pat-tern revealing the crystalline structure of the rhodium nanoparticle. Thenumbers indicate the corresponding lattice plane spacings of rhodium de-fined by the concentric circles.

Figure 2. 1H NMR spectra detected during the gas phase hydrogenation of1,3-butadiene over the Rh/chitosan catalyst with a) normal hydrogen andb) parahydrogen.

&2& www.chemcatchem.org � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 0000, 00, 1 – 6

�� These are not the final page numbers!

K. V. Kovtunov et al.

butene, and less than 1 % of butane. 2-Butene can be formedeither by the isomerization of 1-butene or by the direct 1,4-hy-drogenation of 1,3-butadiene with dissociative surfacehydrogen.

The observation of PHIP effects allows us to conclude that2-butene is formed on the isomerization of the polarized 1-butene. Thus, in spite of almost the same conversion valuesfor 1- and 2-butenes (29 % for 1-butene and 26 % for 2-butene), the observation of PHIP effects for correlated protonsof CH3 and CH groups in 2-butene (Figure 2 b, signals 8 and 7)indicates the existence of the isomerization route, with the po-larization of 1-butene preserved on its isomerization to 2-butene.

The contribution of the pairwise route to the overall reactionmechanism was evaluated by taking into account the theoreti-cal PHIP enhancement factor and the ratio of the polarizedand nonpolarized peaks observed in the experiments. Themethod described earlier[24] allows one to estimate the per-centage of pairwise hydrogen addition for each product of thereaction. It was established that the contribution of the pair-wise hydrogen addition was at least 1 % for 1- and 2-butenes.For butane, no polarization was observed.

The estimated amount of the pairwise fraction in the overallmechanism is not very significant, and the hydrogenationmechanism is mostly dissociative. However, polarization creat-ed in the reaction can be larger than observed. Some polariza-tion is potentially lost owing to the fast nuclear spin relaxationof reaction intermediates and products. Relaxation times forabsorbed hydrocarbon species in porous materials can de-crease to a few microseconds.[25] Therefore, the actual level ofpolarization could be higher, and the pairwise hydrogen addi-tion route should not be neglected.

Notably, the PHIP magnitude of 1H NMR signals of CH2 andCH3 groups of 1-butene and of CH3 and CH groups of 2-butene became much smaller 20 min after the reaction initia-tion, which indicated a decrease in the pairwise hydrogen ad-dition activity of the catalyst. However, the overall activity didnot change significantly.

The change in the original yellow color of the catalyst pelletsto dark gray and the decrease in size indicate that the partialreduction of chitosan surfaces or chitosan matrices took placeduring the hydrogenation reaction.

1-Butyne hydrogenation

It was demonstrated above that the Rh/chitosan catalyst isvery selective for the formation of butenes in 1,3-butadiene hy-drogenation. Therefore, it was interesting to attempt the selec-tive hydrogenation of 1-butyne under the same reaction condi-tions. 1-Butyne was used in the gas phase heterogeneous hy-drogenation with parahydrogen. Similar to 1,3-butadiene gasphase hydrogenation, the Rh/chitosan catalyst is active for 1-butyne gas phase hydrogenation, but only in the first few sec-onds of the reaction, and then the intensity of polarized linesin the 1H NMR spectra and the yield of reaction products de-cline and finally completely vanish after 5–10 min of the reac-tion. Nevertheless, it was possible to detect strong polarization

for 1- and 2-butenes while the catalyst was active. The changein the original color of the catalyst pellets was not observed.This difference in behavior of 1-butyne and that of 1,3-buta-diene could be the result of blocking of active sites by ad-sorbed 1-butyne species.[26]

To avoid the rapid deactivation of the catalyst observedafter 5 min of 1-butyne hydrogenation, the Rh/chitosan pelletsactivated in the hydrogenation of 1,3-butadiene were used in-stead of the fresh catalyst. This activated catalyst is active inthe hydrogenation of 1-butyne, and a strong polarization of 1-butene is observed (see Figure 3 b). The fact that the amountof butane in the gaseous mixture after the reaction was smallindicates that selectivity toward the formation of butenes isa general feature of the Rh/chitosan catalyst. The activation ofthe Rh/chitosan catalyst in the hydrogenation of 1,3-butadieneallows it to be more stable and efficient in the selective hydro-genation of 1-butyne to butenes. In the case of 1-butyne hy-drogenation, PHIP allows us to determine the stereoselectivityof hydrogen addition to the substrate.

The products of both syn- and anti-addition of hydrogen to1-butyne are observed in the 1H NMR spectrum (Figure 3 b,peaks 7 and 8, respectively), with some preference toward syn-addition reflected in the higher polarization intensity of peak 8compared with peak 7. At the same time, a much weaker po-larization was observed for 2-butene (Figure 3 b, peaks 9 and10, respectively), which demonstrated that the product of hy-drogen anti-addition to 1-butyne is formed by its own routeand not by the isomerization of 2-butene to 1-butene.

We have also studied the liquid phase hydrogenation of 1-butyne by using the same high-field PHIP approach (Figure 4).The activity of the Rh/chitosan catalyst was found to be lowerin the liquid phase heterogeneous hydrogenation than in thegaseous phase. Nevertheless, PHIP was observed, and only thesyn-addition of hydrogen proceeded in the pairwise manner(Figure 4, peaks 5 and 4). Thus, the reaction mechanism

Figure 3. 1H NMR spectra detected during the gas phase hydrogenation of1-butyne over the Rh/chitosan catalyst with a) normal hydrogen andb) parahydrogen.

ChemCatChem 0000, 00, 1 – 6 � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemcatchem.org &3&

These are not the final page numbers! ��

Hydrogenation of over a Rh/Chitosan Catalyst

changes significantly with the change in the reaction environ-ment from gaseous to liquid, and if two hydrogen atoms fromthe same hydrogen molecule are transferred together to theproduct, the pairwise route is allowed only for syn-addition.

Conclusions

Herein, the heterogeneous hydrogenation of 1,3-butadieneand 1-butyne over the Rh/chitosan catalyst was studied byusing the NMR and parahydrogen-induced polarization tech-nique. The Rh/chitosan system was a very selective catalyst forthe semihydrogenation of 1,3-butadiene and 1-butyne to 1-and 2-butenes while no significant amount of butane wasformed. Notably, the catalyst demonstrated high activity in thehydrogenation of 1-butyne after its activation in the hydroge-nation of 1,3-butadiene. Therefore, the Rh/chitosan catalystwas used for the catalytic removal of 1,3-butadiene and 1-butyne from gaseous butene streams. Moreover, the syn- andanti-addition of the hydrogen molecule to substrates proceed-ed in a pairwise manner in the gas phase heterogeneous hy-drogenation as was demonstrated by PHIP. However, in theliquid phase hydrogenation of 1-butyne, both hydrogen atomsfrom the same molecule were added to 1-butyne only throughthe syn-addition route.

Experimental Section

Catalyst preparation

The low molecular mass sample of chitosan was supplied by Al-drich (CAS 9012-76-4). Chitosan microspheres were prepared byadding an acidic solution of chitosan (1 g of chitosan in 25 mL of0.3 m CH3COOH aqueous solution) in an aqueous basic solution(NH4OH, 4 m), and the mixture was left overnight for aging. Hydro-gel polymers, obtained by exhaustive water washing until neutralpH, were immersed in the RhCl3(H2O)3 solution (73 mg in 10 mLwater) for 19 h. The resulting submillimetric Rh/chitosan micro-spheres were immersed in successive water–ethanol solutions,

with the volume fraction of ethanol increasing from 10 to 100 %.This gradual replacement of water with alcohol was necessary toprevent the shrinkage that could occur during the hydrogel–alco-gel transition. This hybrid alcogel in which water was removed byethanol was then treated with an ethanolic NaBH4 solution toreduce rhodium located in the polymer matrix. The beads werethen washed with ethanol to remove all physisorbed matter, whichwas followed by ethanol exchange with liquid CO2 in an autoclavewith a quartz window at 50 bar (50,000 kPa) and 10 8C. The CO2-soaked microspheres were then further compressed and heatedabove the critical point of CO2 (31.5 8C, 73.8 bar (7380 kPa)) toenable supercritical CO2 drying of the hybrid materials. Thismethod is the key to obtaining high-surface-area materials, inwhich the dried gel network maintains the structure of its parenthydrogel as no capillary forces that could lead to the collapse ofthe porosity are exerted on the fibrils if CO2 is removed under su-percritical conditions. In this way, materials with a high surfacearea of 480 m2 g�1 were obtained through a Brunauer–Emmet–Teller calculation.

Catalyst characterization

The total rhodium content in the final Rh/chitosan catalyst was2.2 wt % as determined from inductively coupled plasma chemicalanalysis after digesting the Rh/chitosan sample in the HF/HNO3/HCl (1:1:3 w/w) mixture at RT for 24 h.

TEM images were recorded by using a Philips CM300 FEG systemoperating at a voltage of 100 kV. For the sample preparation,a good dispersion of the catalyst in ethanol was achieved through30 min sonication of the suspension. Then, a single drop was de-posited onto a support grid and the solvent was evaporated. Theelectron diffraction pattern of selected area is shown in Figure 1 d.The positions of the diffraction rings are in good agreement withthe literature values of lattice plane spacings of rhodium of a face-centered cubic (fcc) structure (a = 3.803 �).[27] This quantitativeanalysis of the diffraction pattern proves the presence of metallicrhodium crystals in the catalyst. No crystallographic orderingamong the various rhodium grains can be observed in the diffrac-tion pattern. We can calculate the dispersion factor by using theequation D = surface atoms/total number of atoms in the crystal ifmetal nanoparticles are modeled as an fcc crystal lattice.[28] We canestimate the total number (NT) of rhodium atoms in the nanoparti-cle by using the following equation: <d> = 1.105datNT

1/3, in which<d> is the mean diameter of rhodium particles (determined ex-perimentally by using TEM) and dat is the atomic diameter of rhodi-um (0.268 nm); NT = 308 atoms of rhodium in the nanoparticle. Byusing the equation NT = (10 m3�15 m2 + 11 m�3)/3, we can calcu-late the number of atomic shells (m), which is equal to 5. Consider-ing that in the fcc crystal 1 atom is surrounded by 12 atoms andassuming a full-shell close-packed model, the number of externalatoms can be estimated by the equation Ns = 10 m2�20 m + 12, inwhich Ns is the external atoms; Ns = 162 atoms in the surface.Then, the dispersion factor is D = 53 %.

SEM images were recorded by using a JEOL JSM 6300 microscope(Figure 5). The sample preparation required a coating of thesample with a thin layer of the conducting material, carbon.

Hydrogenation experiments

For gas phase hydrogenation experiments, the Rh/chitosan catalystwas placed in a 10 mm NMR tube positioned inside the NMR spec-trometer magnet and maintained at 100 8C throughout the experi-

Figure 4. 1H NMR spectra detected during the hydrogenation of 1-butyneover the Rh/chitosan catalyst in the liquid phase ([D8]toluene).

&4& www.chemcatchem.org � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 0000, 00, 1 – 6

�� These are not the final page numbers!

K. V. Kovtunov et al.

ment. All experiments were performed with parahydrogen, with aninitial ratio of ortho and para isomers of approximately 1:1, andnormal hydrogen, with an initial ratio of ortho and para isomers ofapproximately 3:1. For PHIP experiments, hydrogen was enrichedwith parahydrogen by passing it through a bed of FeO(OH)powder (Sigma–Aldrich) maintained at liquid N2 temperature. A 4:1mixture of hydrogen and substrate (1,3-butadiene or 1-butyne)was supplied to the catalyst through a Teflon capillary extended tothe bottom of the NMR tube. The gas flow rate was set at approxi-mately 360 mL min�1. For liquid phase hydrogenation experiments,the Rh/chitosan catalyst was placed at the bottom of 10 mm NMRtube with [D8]toluene and then the mixture of parahydrogen with1-butyne was bubbled through the solvent. The NMR spectra wererecorded by using a Bruker Avance 300 NMR spectrometer. The1H NMR spectra were detected by using radiofrequency pulseswith a p/4 flip angle without (gas phase hydrogenation) or after(liquid phase hydrogenation) interrupting the gas flow.

Acknowledgements

This work was partially supported by grants RFBR 11-03-93995-CSIC a, RFBR 11-03-00248-a, RFBR 12-03-00403-a, RAS (5.1.1),and SB RAS (#60, 61, 57, 122) ; by the program of support of lead-ing scientific schools (NSh-2429.2012.3) ; and by the program ofthe Russian Government to support leading scientists(11.G34.31.0045).

Keywords: chitosan · heterogeneous · hydrogenation ·parahydrogen-induced polarization · rhodium

[1] a) E. Guibal, Prog. Polym. Sci. 2005, 30, 71 – 109; b) E. Guibal, Sep. Purif.Technol. 2004, 38, 43 – 74.

[2] P. Sorlier, A. Denuzi�re, C. Viton, A. Domard, Biomacromolecules 2001, 2,765 – 772.

[3] A. Primo, F. Quignard, Chem. Commun. 2010, 46, 5593 – 5595.[4] a) D. Zhou, M. He, Y. Zhang, M. Huang, Y. Jiang, Polym. Adv. Technol.

2003, 14, 287 – 291; b) G. Zhao, X. Wu, X. Tan, X. Wang, Open Colloid Sci.J. 2011, 4, 19 – 31.

[5] S. Johannesen, B. Petersen, J. Duus, T. Skrydstrup, Inorg. Chem. 2007,46, 4326 – 4335.

[6] H. Ennajiha, R. Bouhfida, E. Essassia, M. Bousminaa, A. Kadib, Micropo-rous Mesoporous Mater. 2012, 152, 208 – 213.

[7] X. Wang, M. Huang, Y. Jiang, Macromol. Chem. 1992, 59, 113 – 121.[8] D. Macquarrie, J. Hardy, Ind. Eng. Chem. Res. 2005, 44, 8499 – 8520.[9] E. Slivinskii, N. Kolesnichenko, Russ. Chem. Bull. 2004, 53, 2449 – 2454.

[10] M. Adlim, M. Bakar, K. Liew, J. Ismail, J. Mol. Catal. A 2004, 212, 141 –149.

[11] A. El Kadib, K. Molvinger, M. Bousmina, D. Brunel, Org. Lett. 2010, 12,948 – 951.

[12] A. El Kadib, A. Primo, K. Molvinger, M. Bousmina, D. Brunel, Chem. Eur. J.2011, 17, 7940 – 7946.

[13] H. Arnold, F. Dçbert, J. Gaube in Handbook of Heterogeneous Catalysis(Eds. : G. Ertl, H. Knçzinger, J. Weitkamp), Wiley-VCH, Weinheim, 2008,pp. 2165 – 2186.

[14] G. C. Bond in Metal-Catalysed Reactions of Hydrocarbons (Fundamentaland Applied Catalysis), Springer, 2005, pp. 291 – 395.

[15] G. A. Olah, �. Moln�r in Hydrocarbon Chemistry, Wiley, New York, 2003,pp. 185 – 194.

[16] a) K. Kovtunov, I. Beck, V. Bukhtiyarov, I. Koptyug, Angew. Chem. 2008,120, 1514; Angew. Chem. Int. Ed. 2008, 47, 1492; b) V. Zhivonitko, K. Kov-tunov, I. Beck, A. Ayupov, V. Bukhtiyarov, I. Koptyug, J. Phys. Chem.2011, 115, 13386 – 13391.

[17] K. Kovtunov, V. Zhivonitko, A. Corma, I. Koptyug, J. Phys. Chem. Lett.2010, 1, 1705 – 1708.

[18] K. Kovtunov, I. Beck, V. Zhivonitko, D. Barskiy, V. Bukhtiyarov, I. Koptyug,Phys. Chem. Chem. Phys. 2012, 14, 11008 – 11014.

[19] a) S. Duckett, C. Sleigh, Prog. Nucl. Magn. Reson. Spectrosc. 1999, 34,71 – 92; b) C. R. Bowers in Encyclopedia on nuclear magnetic resonance,Vol. 9, Wiley, New York, 2002, pp. 750 – 770.

[20] a) C. Bowers, D. Weitekamp, J. Am. Chem. Soc. 1987, 109, 5541 – 5542;b) C. Bowers, D. Weitekamp, Phys. Rev. Lett. 1986, 57, 2645 – 2648.

[21] a) J. Natterer, J. Bargon, Prog. Nucl. Magn. Reson. Spectrosc. 1997, 31,293 – 315; b) R. Green, R. Adams, S. Duckett, R. Mewis, D. Williamson, G.Green, Prog. Nucl. Magn. Reson. Spectrosc. 2012, DOI: 10.1016/j.pnmrs.2012.03.001.

[22] I. Koptyug, V. Zhivonitko, K. Kovtunov, ChemPhysChem 2010, 11, 3086 –3088.

[23] a) L. Bouchard, S. Burt, M. Anwar, K. Kovtunov, I. Koptyug, A. Pines, Sci-ence 2008, 319, 442 – 445; b) V. Telkki, V. Zhivonitko, S. Ahola, K. Kovtu-nov, J. Jokisaari, I. Koptyug, Angew. Chem. 2010, 122, 8541 – 8544;Angew. Chem. Int. Ed. 2010, 49, 8363 – 8366.

[24] K. V. Kovtunov, I. V. Koptyug in Magnetic Resonanse Microscopy. SpatiallyResolved NMR Techniques and Applications (Eds. : S. Codd, J. Seymour),Wiley-VCH, Weinheim, 2008, pp. 101 – 115.

[25] Q. Xu, T. Eguchi, H. Nakayama, N. Nakamura, J. Chem. Soc. FaradayTrans. 1996, 92, 1039 – 1042.

[26] P. Sch�fer, N. Wuchter, J. Gaube, Stud. Surf. Sci. Catal. 2000, 130, 2051 –2056.

[27] International Center for Diffraction Data, PDF file 05-0685.[28] A. Abad, A. Corma, H. Garc�a, Chem. Eur. J. 2008, 14, 212 – 222.

Received: June 27, 2012

Published online on && &&, 0000

Figure 5. SEM image of the Rh/chitosan catalyst.

ChemCatChem 0000, 00, 1 – 6 � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemcatchem.org &5&

These are not the final page numbers! ��

Hydrogenation of over a Rh/Chitosan Catalyst

FULL PAPERS

D. A. Barskiy, K. V. Kovtunov,* A. Primo,A. Corma, R. Kaptein, I. V. Koptyug

&& –&&

Selective Hydrogenation of 1,3-Butadiene and 1-Butyne over a Rh/Chitosan Catalyst Investigated byusing Parahydrogen-InducedPolarization In pairwise fashion: Hydrogenation of

1,3-butadiene and 1-butyne over theRh/chitosan heterogeneous catalyst ingaseous and liquid phases is investigat-ed. Hydrogenation is very selective and

no significant amount of butane isformed. The syn- and anti-addition ofhydrogen to 1-butyne are investigatedby using the parahydrogen-inducedpolarization technique.

&6& www.chemcatchem.org � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 0000, 00, 1 – 6

�� These are not the final page numbers!