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(solution) literature review summary of the project "Selective

literature review summary of the project ?Selective hydrogenation of acetylene?. It?s 8-12 pages double spaced with font size of 12. The reference section will single spaced.  Review examples are attached.

I will give you 80 $ and if you do good on it I am willing to give twice more then 80$

Review Modern Trends in Catalyst and Process Design for Alkyne




Micaela Crespo-Quesada, Fernando Ca?rdenas-Lizana, Anne-Laure Dessimoz, and Lioubov Kiwi-Minsker*


Group of Catalytic Reaction Engineering, E?cole Polytechnique Fe?de?rale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland


ABSTRACT: This review provides an overview of the recent


achievements in catalytic process development for alkyne hydrogenations. It underlines the necessity of simultaneous optimization


over di?erent length scales from molecular/nanoscale of active


phase, up-to macro-scale of catalytic reactor design. One case


study, the hydrogenation of 2-methyl-3-butyn-2-ol, is analyzed in


detail to illustrate the practical application of this approach. Finally,


it presents the personal view of the authors concerning the new


trends and paths available in the ?eld.


KEYWORDS: alkyne, hydrogenation, catalyst design, support e?ect, reactor design 1. INTRODUCTION


Sustainable processing with minimal environmental impact has


been recognized as one of the major challenges of this century.1


As a result of the severe restrictions in environmental


legislation, the chemical industry is now undergoing a


progressive rede?nition. Catalytic technology, as a fundamental


tool for green chemistry, has an unprecedented enabling


potential for sustainable production. Heterogeneous catalysts


are of utmost importance in the ?ne chemical industry. The


typical design in these systems is based on an active phase, main


responsible for the catalytic performance (activity and


selectivity), immobilized on a suitable support. This avoids


agglomeration of the active species during chemical reaction


and enables an easy catalyst recovery. The conventional


methodology applied for catalyst optimization has been an


empirical ?trial-and-error? approach which results, at best, in


slight or incremental improvements of their performance.


Moreover, it is greatly based on speculation and is, in practice,


laborious and time-consuming. With the concomitant advance


in theoretical understanding and the development of computational power, a new era of rational catalyst design (RCD) is


dawning.2 This approach is based on a multidisciplinary


combination of new advances in synthesis, characterization,


and modeling with the ultimate aim of predicting the catalyst?s


behavior based on chemical composition, molecular structure,


and morphology.3


Given the multicomponent nature of an heterogeneous


catalyst, it is necessary to bear in mind that its overall


performance depends not only on the contribution of the active


component, but also on other factors such as the interplay


between the catalytically active species and the surrounding


environment, and the type of chemical reactor where the


process is carried out (Figure 1). Therefore, RCD must span


over multiple levels of complexity, from the molecular or


nanoscale involving the design of the active sites to the macroscale design of the industrial reactor where the catalyst is bound


© 2012 American Chemical Society Figure 1. Rational catalyst design spans over several levels of scale and


complexity.2 to operate, since they are in direct interaction in?uencing the


overall performance.


The catalytic partial hydrogenation (semi-hydrogenation) of


alkynes is of special relevance in the bulk and ?ne chemical


industries4 since it is an e?cient method for production of


alkenes. This process is conventionally performed over


quinoline-promoted CaCO3 supported Pd catalyst partially


poisoned with lead, which is known as Lindlar?s catalyst.5,6


However, the application of this conventional catalytic system


to alkyne hydrogenations is sometimes problematic because of


selectivity issues (overhydrogenation to alkanes), limited


catalyst robustness, and reuse. Moreover, catalyst deactivation,


the presence of toxic lead, and the need for the addition of an


Received: May 4, 2012


Revised: June 29, 2012


Published: July 11, 2012


1773 | ACS Catal. 2012, 2, 1773?1786 1774 10?100; 0?100


100; 85


2?100; 0?100 1 ; 278?323 1 ; 348


1; 348


0.9 × 10?3?1 ; 308?373 0?100; 0?92


5?100; 30?100 1 ; 373?523


1 ; 423?523


3?100; 20?99.5


65?69; 40?74


58?88, 10?100


3?100; <5?90


35?100; 25?60 100;




15?80 ; 25?98 10?100 ; 48?100


0?63; 18?100 1 ; 273?298


1 ; 363?623 1 ; 363?553


0.06?0.20; 293?333


0.07?0.11; 313?493


1; 255?293


1 ; 373?513 5?100; 2?98 100; 25?80


50; 49?76


0?100; >95 1 ; 523


1 ; 298


1 ; 283?353 1 ; 423 10?25 ; 35?85 1 ; 343?423 <5?99; 60?85 <5?100; 0?100 1?16 ; 303?453 1 ; 298?613 0?100; 45?100 X (%); SCC (%) 1 ; 298?673 P (bar) ; T (K)


powder vs [structured] support(s) reactor 26 24,25 17




19?23 14?16 11?13 27,28


29,30 ?xed-bed microreactor


?xed-bed microreactor


continuous-?ow microreactor


(CO) ?-Al2O3; CaCO3; HT


CaCO3 (Lindlar)


?-Al2O3; ZnO; SiO2; Al2O3; CNTh Pd; Pd?Pb; Cu; Ni ; Cu?Ni




Pd black; Pd ?-Al2O3 Pd-Xg 43




44?47 42 ?ow reactor Al2O3; SiO2


SiO2 d 34








40,41 dynamic ?ow


static constant volume system


static constant volume system


glass ?ow


?xed-bed ?ow microreactor




pumice 31,32


17,33 ?xed-bed microreactor


?xed-bed microreactor Ni?Al ; Cu


Cu ; Cu?Fe; Cu?Al ; Cu?


Ni?Fe; Cu?Ni?Al






Ni; Cu; Ni?Cuf


Pt ; Pt?Ru


Cu ZrO2; SiO2; Al2O3


SiO2; MgO; (?-,?)Al2O3; ZrO2; TiO2;


Fe2O3; SiO2?Al2O3




HTd; SiO2; Al2O3 ref.


8?10 pulse-?ow reactor


dynamic ?ow/pulse-?ow reactor Pd ; Pt


Cu ; Auf


(CO) ?ow reactor ?-Al2O3 Au ICe; Al2O3 d [CNF; ACF]c Pd?Gae ; Pd ; Pd?Age gas circulation system/single pass ?ow


reactor/?xed-bed microreactor


?ow reactor/microreactor HT


active carbon


pumice; SiO2; Al2O3; MgAl2O4 TiO2; Al2O3 Al2O3; ?-Fe2O3; CeO2 Cu?Fe;Cu?Ni?Fe




Pd ; Ni?Zn ILa, PVPb,


KBr stabilizer


(modi?er) meso-level/macro-level pulse-?ow reactor/jacketed tubular ?xed-bed




?xed-bed microreactor


nongradient ?ow


gradientless microreactor/tubular ?xed-bed




pulse-?ow reactor Au; Ag ; Pd; Pd?Au; Pd?Ag;




Pd Au metal nanolevel a IL = ionic liquid. bPVP = poly(vinylpyrrolidone). cCNF = carbon nano?bers, ACF = activated carbon ?bers. dHT = hydrotalcite. eIC = intermetallic unsupported compound. fcatalysts provided by the


World Gold Council. gX = Ge, Sb, Sn, Pb. hCNT = cabon nanotubes. 1-Pentyne but-1-yne; 1-butene3-yne


2-methyl-1-buten-3yne propyne+propadiene


but-1-yne acetylene and








propyne acetylene+ethylene acetylene reactant(s) reaction Table 1. Compilation of Literature on Gas-Phase Alkyne Hydrogenation ACS Catalysis


Review | ACS Catal. 2012, 2, 1773?1786 [100]


40?100 ; 85?100


10?99 ; 77?99 [>95]


96?100 ; 81?97




95 ; 97.5


80 ; 15?59 [94]


100 ; 91?99 100 ; 65?85 2?10 ; 308?348 1 ; 328?337 5 ; 333


2?6.7 ; 308?343


5 ; 343


1?6 ; 303?323


2.4 ; 323 1775 15 ; 80


8?100 ; 83?91 1 ; 283


7 ; 333 metal PVPc, Surfactants, ILi (Rh, Ru,


Ag, Cu, Pb)


PVPc, Na2MoO4, AOTa, CTABe


(S-CCl, quinoline)


(pyridine) Pt


Rh (Sn)


PVPc (PPh3) reactor semibatch microreactor


semibatch vibration reactor


semibatch silica, [monoliths], CNFd, SiO2


graphite oxide, C, HTp, Al2O3, Montmorillonite


C, CNTq, ACr [Si foam] ?-Al2O3, MCM-41f




Nylon, C semibatch


Fisher?Porter bottle microreactor semibatch








semibatch multibatch


membrane semibatch






semibatch Fisher?Porter


bottle vibration reactor


semibatch semibatch




vibration reactor TiO2




CaCO3 (Lindlar)


?-Al2O3, C


- CaCO3, C C, SiO2, Al2O3, TiO2


TiO2, AMMSiTig


TiO2, Al2O3, CaCO3


CaCO3 (Lindlar)


C, CaCO3, Al2O3, CeO2, SBA-15j, MCM-48j,


MSU ?-Al2O3k, graphite oxide








phenanthroline, PVPc (Bi, Pb) powder vs [structured] support(s)


[CNF/SMF]d, Al2O3,


CaCO3 (Lindlar)


MCM-41f stabilizer (modi?er) meso-level/macro-level



AOTa, bipyb, PVPc (Bi, Pb) Pd PdZn










Pt, Rh, Ru, Pd PVPc


and Ni




(Cu, quinoline, KOH)




CTABe, SDSo ((nC4H9)4NBH4)


Pd Pd PdOxHy








Pd Pd




Pt nanolevel ref. 84


85 78?83 72?75


59,76?78 67








71 61?66 53








51,57?60 48?51




52 f a AOT = sodium di-2-ethylhexylsulfosuccinate. bbipy = bipyridine. cPVP = poly(vinylpyrrolidone). dCNF = carbon nano?bers, SMF = sintered metal ?bers. eCTAB = cetyltrimethylammonium bromide.


Mesoporous silica. gAMMSiTi = amorphous microporous titania-silica mixed oxide. hInformation not provided. iIonic liquids. jMesoporous silica. kMesoporous gamma alumina. lS-CC = Sulfur containing


compound. mSBCR = staged bubble column reactor. nPEO-b-P2VP = poly(ethylene oxide)-block-poly-2-vinylpyridine. oSDS=Sodium dodecyl sulfate. pHT= hydrotalcite. qCNT=carbon nanotubes.




AC=activated carbon. 4?100 ; 10?100 [>95] 1?20 ; 283?333 phenylacetylene 6 ; 95 [54?97]


4?100 ; 95?100 [91?99] 1?2.3 ; 298


1?8 ; 283?303 h 10?100 ; 20?95


7?90 ; 63?99 5 ; 353


1 ; 333?393


1 ; 298


1 ; 298


1?2.8 ; 283?298 X (%) ; SCC (%) [Y(%)]


85?100 ; 98.5


99 ; 87


33?78 ; 96?99 P (bar);T (K) 1?10.5 ; 298?303


10.5 ; 303


1 ; 298 MPY


4-octyne 2-butyne-1,4-diol 3-hexyne 3hexyn-1-ol


MBY 1-hexyne 1pentyne


2-hexyne 1-hexyne reactant reaction Table 2. Compilation of Literature on Liquid-Phase Alkyne Hydrogenation ACS Catalysis


Review | ACS Catal. 2012, 2, 1773?1786 ACS Catalysis Review amine modi?er are the main drawbacks of this catalytic system.7


Therefore, during the past few years a signi?cant number of


publications were devoted to alkyne hydrogenation processes.


Given the requirement of the simultaneous consideration of


di?erent levels for optimum catalytic process design, this review


is focused on the analysis of the di?erent scale lengths (nano,


micro, and macro) applied to the catalytic selective CC to


CC hydrogenation with special emphasis on the literature


published over the past decade.


Instead of merely providing an enumeration of the articles


dealing with catalytic semi-hydrogenation over the di?erent


scale lengths, a representative compilation of studies is given in


Tables 1 and 2 for gas and liquid phase operations, respectively.


The information shown serves to illustrate (a) the range of


reactions that have been investigated; (b) the operating


temperatures and pressures; (c) the catalytic performance in


terms of activity (presented as conversion (X)) and product


distribution (in terms of selectivity (Si) or yield (Y)); (d) the


nature of the catalytic systems that have been investigated at


di?erent scale lengths, that is, nano (metal and precursor/


stabilizer), meso (support), and macro-level (reactor).


Of direct relevance to this work, we should mention the


overview on hydrogenation of carbon?carbon multiple bonds


published by Molna?r and co-workers in 2001,86 which has since


been supplemented by the reports of Borodzin?ki and Bond87,88


on selective hydrogenation of ethyne in ethene-rich streams


over palladium catalysts, and the recent examination of the


theoretical work to elucidate the catalytic properties required


for selective alkyne hydrogenation in mixtures by Lo?pez and


Vargas Fuentes.89 The critical role of a combined (catalyst,


process and reactor) design strategy for optimizing heterogeneous catalysis was illustrated in a review by Sie and Krishna in


1998,90 which has been since covered in more recent




This Review contains two main parts. First, a critical analysis


of the pertinent literature dealing with catalyst design for


selective CC to CC hydrogenations across the three scale


lengths previously reported is provided and new trends are


underlined. In the second part, a case study, the hydrogenation


of 2-methyl-3-butyn-2-ol (MBY) is presented for illustrative


purposes. Finally, the Review ends with a consideration of


directions for the future. gies.93 Indeed, despite the faster ole?n hydrogenation over Pd


with respect to the acetylenic counterpart, the reduction of the


latter is favored as a result of the increased adsorption strength,


that is, the selectivity has a thermodynamic nature.94


Several factors have been proposed to control a catalyst?s


performance in alkyne hydrogenations involving the di?erent


scale lengths of the catalyst architecture:


? Nanoscale, where the e?ect of the morphology of the


active nanoparticles is considered through the observation of


metal dispersion,14,20,47,48,63,64,79,87 shape e?ects,64,71 and/or


the presence of speci?c types of active sites.61 Surface


modi?cation by the reaction medium is also important at this


stage of optimization.16,44,95


? Mesoscale, where the interactions between the active metal


nanoparticle and its intimate environment is assessed through


the modi?cation by alloying, 46,63 the involvement of


additives,32,49,69,96 and/or metal/support interactions.28,30


? Micro/milli/macro-scale design where the support


structure and morphology are tailored according to the


particular requirements of the reaction in conjugation with


the development of a suitable chemical reactor.68


2.1. Active Phase Optimization: Nano/Meso-Level.


One of the key factors a?ecting the catalytic behavior of the


active phase is the interplay between its properties and the


reacting molecules. Therefore, to achieve a fundamental


understanding of catalytic reactions, surface-science experiments44?47 and theoretical calculations23,33,93,95,97 are required


to provide insights into surface dynamics and the nature of the


adsorbed species. A quintessential work steering in this


direction in which density functional theory (DFT) calculations


are used to identify potential new catalysts for the selective


hydrogenation of acetylene was recently published.23 The


authors proposed Ni?Zn as an optimal alternative formulation


with respect to the conventional Pd-based active phase, which


was subsequently corroborated experimentally. Despite the


undeniable usefulness of such work, the results should be


somehow considered carefully since the formation of oligomers


during acetylene hydrogenation was neglected in their




Although surface and theoretical analyses can provide an


additional tool for catalyst optimization, there is still a gap in


terms of expected and obtained response when moving to real


catalytic systems. Nanoparticle morphology has been identi?ed


as a key characteristic linked to the active phase for the


hydrogenation of alkynes where di?erences in catalytic


performance have associated to mechanistic, electronic, and/


or geometric e?ects.98?100 The incorporation of a second metal


or speci?c compound has also proved an e?ective means to


in?uence selectivity and activity in CC hydrogenation.


This section reviews the results of nanoscaled studies for


catalytic alkyne hydrogenations considering ?rst the active


phase alone, particularly the issue of structure sensitivity, and of


active phase modi?cation under reaction conditions. Second,


the modi?cation of the active nanoparticles through alloying


and additives is also reviewed.


2.1.1. Structure Sensitivity. The morphology (shape and


size) of the active phase (metal nanoparticles) is among the


structural features that have a greater impact on catalytic


performance in alkyne hydrogenation.101 In the 1960s it had


become clear that the rate of certain catalytic reactions,


expressed per unit area, or turnover frequency (TOF), was


independent of the metal particle size and were de?ned as


structure-insensitive. On the other hand, if a correlation between 2. MULTI-LEVEL APPROACH FOR CATALYTIC ALKYNE




The selective CC hydrogenation (to the correspondent


ole?n) is an important process in industry for both the


production of intermediates in the manufacture of ?ne


chemicals,63 and in bulk chemistry, for example, ethylene


hydrogenation during the synthesis of polyethylene (global


annual production of 50 million tons92) and the puri?cation of


alkene streams for the upgrade of low weight fractions from


stream crackers.


The open literature on selective alkyne hydrogenation


reports the process carried out in both gas (see Table 1) and


liquid-phase (see Table 2). It can be seen that this type of


reaction has been primarily carried out over powdered catalysts


based on monometallic Pd and, to a lesser extent, Pt-, Ni-, Cu-,


and Au-based catalysts where the last two metals show promise


in terms of achieving high selectivity.9,17,32 Focusing on Pd as


the metal with the best performance for this type of


reaction,5?7 the increased alkene selectivity over Pd can be


associated with the distinct alkyne/alkene adsorption ener1776 | ACS Catal. 2012, 2, 1773?1786 ACS Catalysis Review (nanohexagons vs nanospheres) but dependent on the number


of Pd atoms located on (111) planes.64


We can therefore conclude that an accurate identi?cation of


the active sites responsible for the catalytic performance would


actually imply a redef inition of the terms ?size? and ?shape


e?ects? to ?structure e?ect? arising from the relative amount of


active sites on the nanoparticle surface regardless of the shape


or size of the crystallite. This is illustrated in recent studies for


the hydrogenation of 2-methyl-3-butyn-2-ol where it has been


shown that the dependency between TOF and particle size


disappeared when only Pd111, that is, the active sites for the


reaction, is taken into account.64,65 This ?nding is complemented by our recent work61 where, for the same reaction, we


have shown for a series of Pd nanoparticles with well-de?ned


shapes and sizes (see Figure 2) that two type of active sites, that TOF and metal dispersion could be established, the reaction


was then referred to as structure-sensitive. It is however more


likely that every reaction will show a degree of structure


sensitivity, depending on the stringency of its requirements for


an active center.102 It is worth mentioning that a variation in


shape also implies important morphological di?erences: cubes


only present (100) plane atoms, octahedra solely (111) plane


atoms whereas a mixture of both can be found in cubeoctahedra (sphere). This will provoke another type of


structure-induced e?ect, that is, a shape e?ect, particularly if


each type of surface atom possesses a di?erent reactivity.


The ?rst study tackling the issue of nanoparticle size effects


was published in 1983 by Boitiaux et al.103 Since then, we have


come to realize that a key requirement for structure sensitivity


studies calls for the preparation of catalysts which di?er only in


particle size and/or shape. Typical catalysts are based on


supported metal nanoparticles where size control of the metal


phase has been achieved by modi?cations in the nature of the


precursors, supports or preparation conditions. As a result, not


only size but other important chemical and structural properties


of the catalyst that a?ect catalytic performance are also


modi?ed. Therefore, the early data published on size e?ects


in the selective hydrogenation of multiple carbon?carbon


bonds are rather controversial, although some consensus


emerges pointing toward higher activity for larger particles,


that is, an increase in metal dispersion decreases


TOF.14,18,20,47,48,64,65,79 Small nanoparticles (less than 2 nm)


are characterized by a predominance of surface atoms of low


coordination number characterized by an electron density


de?ciency. The low activity can be explained on the basis of


strong complexation of the surface atoms by the highly


unsaturated electron-rich alkyne. Furthermore, it is known that


Pd can absorb hydrogen at room temperature when the partial


pressure exceeds 0.02 atm resulting in the formation of ?palladium hydride.104 Hydride formation is the result of


hydrogen di?usion in the Pd crystallite structure to occupy


the available octahedral ?vacancies? in the metal lattice. The


relationship between the number of Pd atoms in the bulk


crystal with respect to those on the surface, decreases with


decreasing particle size to attain a limiting value (<2.5 nm),


where Hab/Pd is close to zero.105,106 The in?uence of this phase


in alkyne hydrogenation is still rather controversial with reports


in the literature suggesting that it is responsible for the direct


alkane formation99 while others did not observe this


detrimental e?ect,100 although a recent publication reports


theoretical calculations showing the great importance of


subsurface species in alkyne hydrogenations.95


In terms of Pd nanoparticle shape ef fects, there is limited


work available in the open literature, particularly for alkyne


hydrogenation.107,108 Unlike size, shape control was only


recently achieved in a straightforward manner thanks to


colloidal techniques.107?109 The advances in colloidal preparation of metal nanostructures open new opportunities in the


study of structure-sensitive reactions since they provide


catalytic metal particles with size or shape variation without


other perturbations, thus rendering them excellent materials


suitable for catalytic investigations. For example, Telkar et al.71


concluded a dependency between shape and activity (in terms


of TOF) for cubic and spherical nanoparticles in the


hydrogenation of 2-butyne-1,4-diol. In contrast, in the


hydrogenation of 2-methyl-3-butyn-2-ol catalytic performance


was found to be insensitive to the nanoparticle shape Figure 2. Types of active sites in the hydrogenation of 2-methyl-3butyn-2-ol (MBY). Plane atoms, regardless of their crystallographic


orientation, ?1 and low coordination or edge atoms, ?2. Reprinted with


permission from ref 61. Copyright (2011) American Chemical Society. is, plane and edge atoms, are responsible for the catalytic


performance. Indeed, the existence of two or more di?erent


kinds of active sites responsible for observed size and/or shape


e?ects has not been thoroughly discussed in the literature.102


This fundamental knowledge has a signi?cant potential for


catalyst optimization for industrially important hydrogenations.


The study of the reaction on well-de?ned catalysts allows the


full kinetic description of the system, and it therefore enables


the prediction of the size and shape of the active phase to


maximize catalytic e?ciency.61 Only with the new developments in the nanoscaled architecture of the catalyst with the


blooming of simple and versatile colloidal methods of


nanoparticle preparation were these achievements possible.


Additional complications can arise for reactions in gas


(relative to liquid) phase operation as a result of the more


demanding conditions, for example, increased reaction temperatures, which can in?uence the surface chemistry of the


nanoparticles. Much e?ort has been devoted in this direction to


the investigation of the structure sensitivity of acetylene


hydrogenation as illustrated in Table 1.14,15,110 However, it is


now almost unanimously accepted that the observed di?erences


are linked to the formation of a carbonaceous overlayer on the


surface of Pd.28,39,44,47 This has been con?rmed by both


experimental (XPS44) and theoretical (DFT calculations111)


analyses. It was ?rst suggested that the deposited carbon was


only a selectivity modi?er through site isolation envisaging sites


of di?erent sizes between carbon deposits.20?22,39,112 However,


this has been recently revoked in studies showing the formation


of carbide species in the subsurface region of the crystallite that


prevent the dissolution of hydrogen in the bulk of the


nanoparticle,44,45,47,95 that is, eliminates the source of


unselective hydrogenation (Figure 3).44,47 It must be however


1777 | ACS Catal. 2012, 2, 1773?1786 ACS Catalysis Review Catalyst Modi?ers. The incorporation of stabilizing


agents, for example, surfactants, polymers, and dendrimers107?109,116 (see Table 2) during the preparation process


is required for the stabilization of the inherently thermodynamically and kinetically unstable solutions of nanoparticles


subsequently used for catalysis. Moreover, shape control


implies the use of molecular capping agents which selectively


adsorb to one speci?c crystal plane, thus favoring the addition


of metal on the weakly bonded facet and directing the growth


of the nanoparticle.109 Despite the extensive cleaning


procedures applied to the obtained nanoparticles, it is common


to ?nd traces of the stabilizing and capping agents which


modify the true catalytic behavior of the metal.


The presence of PVP as stabilizer for Pd,16,51 Pt,55 and Rh85


has been associated with improved selectivity toward the target


alkene because of the electronic modi?cations of Pd induced by


N-containing species. This is in good agreement with results


obtained over catalysts permanently modi?ed with bipyridinebased ligands,49 phenanthroline-based ligands,56 and copolymers.69


Surfactant stabilizing agents58,64,117 have also been used in


alkyne hydrogenations where catalytic performance has been


correlated with the charge and the alkyl chain length.58


Equivalent activity was obtained with CTAB and AOT, in the


selective hydrogenation of MBY64 while lower rates were


reported for PVP (relative to AOT)101 and ascribed to the


stronger interaction of the latter wi...


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