Propylene Oxide Formation on a Silica Surface with Peroxo Defects

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

A: Environmental, Combustion, and Atmospheric Chemistry; Aerosol Processes, Geochemistry, and Astrochemistry

Propylene Oxide Formation on a Silica Surface with Peroxo Defects: Implications in Astrochemistry Marco Fioroni, Andrea Kelly Tartera, and Nathan J. DeYonker J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b04955 • Publication Date (Web): 29 Oct 2018 Downloaded from http://pubs.acs.org on November 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Propylene Oxide Formation on a Silica Surface with Peroxo Defects: Implications in Astrochemistry Marco Fioroni,∗ A. Kelly Tartera, and Nathan J. DeYonker∗ 213 Smith Chemistry Building, The University of Memphis, Memphis, TN, USA, 38152 E-mail: [email protected]; [email protected] Phone: +1 (901) 678-2029

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract The formation of the chiral molecule propylene oxide (CH3 CHCH2 O) recently detected in the inter-stellar medium (ISM) is proposed to take place on an amorphous silicate grain surface where peroxo defects are present. A computational analysis conducted at the DFT and MP2-F12 levels of theory on a neat amorphous silica model supports such a hypothesis resulting in: a) strong thermodynamic driving forces and low activation energies allowing the synthesis of CH3 CHCH2 O at low temperatures; b) chemical defects on silica surfaces promoting heterogeneous catalysis of the increasing molecular complexity found in interstellar and circumstellar medium; c) chemical defects that have implications on understanding how processing phases modify the nature of the reactive groups on a silica surface affecting the surface catalytic activity.

Introduction The recent detection of chiral propylene oxide (CH3 CHCH2 O) in the interstellar medium (ISM) 1 and other complex organic compounds found in meteorites 2–4 and comets 5 are supporting the evolution of astrochemical models. The importance of propylene oxide is dual: its chirality (as the first chiral molecule found in space 1 ) and as part of the epoxides chemical class where reactions with other substrates are very interesting (i.e. epoxides are potent electrophiles undergoing nucleophilic attack). For example, epoxide reactions with H2 O results in the corresponding glycol (propylene oxide → propylene glycol) while reaction with a hydride produces the corresponding alcohol (propylene oxide → propanol). Additional nucleophiles can react with epoxides like alcohols, amines or thiols resulting in a large spectra of organic compounds, suggesting a role of epoxides as flexible chemical tools capable of increasing the molecular complexity found in space 6 . Together with sophisticated gas-phase homogeneous reactions, gas-phase/solid(surface) heterogeneous chemistry involving dust grains 7 are receiving greater attention due to their potential catalytic properties. Between the families of dust particles detected in space, sili2


Page 2 of 22

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cate dust particles 8 can work as efficient heterogeneous catalysts 7,9,10 . Their catalytic properties are partially due to the surfaces covered with “defects” of geometrical (i.e. dislocations on a crystalline surface) and/or chemical origin (i.e. charges, free valences and heteroatoms). In the inter-stellar medium (ISM), the detected silicate crystallinity vs. amorphous mass fraction of 0≤x≤5 % 11,12 suggests supernova shock-waves influence the re-processing phase of the starting crystalline state, of which 10 % are nanoclusters (≤1.5 nm) 13 . The amorphous state has received attention via experimental analysis of oxygen diffusion-desorption 14 , oxygenozone formation 15 and water synthesis 16 . Because of the interest in surface chemical defects, which are known to play an important terrestrial role in neat silica surfaces from heterogeneous phase catalysis to the “aging” of electronic devices 17–19 , a simplified computational model based on a silsesquioxane cage (Figure 1) reproducing an amorphous silica state is used to simulate an amorphous “defective” silicate surface.

Figure 1: The adopted silsesquioxane model representing an amorphous surface with a radical oxygen and two vicinal silanol groups In this simplified model, the main SiO4 or [(SiO2 )x ] units and skeleton are still present, making the chemistry of a pure silica model reasonably transferable to a silicate, (which is the most abundant mineralogical form in space) when only the SiO chemistry is considered. Though silica is not a major constituent of the interstellar medium (ISM), its presence has been found in proto-planetary disks of T Tauri stars 20 . Such a chemical defective model was proposed to partially explain the H2 abundance found in space, performing H2 synthesis from atomic hydrogen 9,21 . Hydration of silica/silicate surfaces results often in an enrichment 3



of SiOH units, as analyzed in a recent study correlated to H2 formation on silicate nanoclusters 22 and methanol formation 23 . In particular, a crystalline or amorphous silica surface is covered by free, reactive silanol groups (Si-OH) 24,25 whose surface density is temperature dependent and related to the history/treatment of the material 19,21 . Due to the harsh conditions (T and radiation) and reprocessing phases 26,27 experienced in space by the silicate dust grains, surface based free silanol groups reasonably exist with appreciable lifetimes. However, on a silica surface not only silanols or charged groups 28 but other highly reactive chemical defects of radical character such as (SiO)x -Si• or (SiO)x -O• 29 can be present. When a silica surface is irradiated with ion beams or UV light under vacuum, the surface is covered by oxygen deficient centers (ODC) as an outcome of the reaction: (O)Si-O-Si(O) → (O)Si-Si(O) + O2 ; non-bridging oxygen hole centers (NBOHCs) derived by a homolytic cleavage of a silanol group: (O)Si-OH → (O)Si-O• + H and peroxy-radicals (PORs) can be formed by the reaction of two NBOHCs, if oxygen is not present 17–19,30 . Furthermore, amorphous silica are receiving great attention due to their dual properties as catalysts and ligand donors: as catalysts with their free oxo groups on the surface and as ligand donors for single atom and/or clusters of transition metals 31 . Focusing our analysis on the (SiO)x -O• radical in the presence of atomic oxygen, a final highly reactive peroxo radical such as (SiO)x -Si-O-O• will be formed, ready to couple with chemical species nearby. In the case of a (SiO)x -Si• radical, the reaction with an O will lead to the (SiO)x -O• radical that is able to react with a second O atom, resulting in the final peroxo group. The introduced model silsesquioxane 9 is used to show peroxo formation and reactivity on an amorphous silica surface with the (SiO)x -O• unit near two vicinal silanols, working as efficient H bond donor/acceptors. We note that a more realistic description of the cold dense cloud physico-chemical conditions may be represented by a computationally unrealistic tri-phasic system composed of a silicate surface-amorphous solid water (ASW)gas phase interface. In our simpler bi-phasic model, the main assumption lies in treating the intermediate ASW as a sieve affecting the reaction via a diffusion limited and molecular

4


Page 4 of 22

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


weight cut-off mechanism. In fact, under the considered reaction temperature (≈10 K), high density ASW (Ihd , ρ=1.16 g/cm3 ) is the main form. Depending on the growth mechanism when T≤130 K, ASW Ihd is expected to be porous 32–34 . The following proposed mechanism will be discussed, first with free oxygen on a silica surface reacting with atomic oxygen: I) (SiO)x -Si-O• + O (3 P) → (SiO)x -Si-O-O• Such a reaction possesses astrochemical interest due to the high reactivity of the peroxo group and its barrier-less formation (see Supp. Info., Figure S1). In fact EPR and optical absorption characterization of peroxo radicals on silica surfaces have shown that reaction I occurs with very fast kinetics at 77 K 19 . Once a peroxo group is formed, a nearby adsorbed organic molecule like propene (H3 C-CH=CH2 ) 35 can be easily oxidized to propylene oxide by a sequence of reactions such as (Figure 2): II) (SiO)x -Si-O-O• + propene → [(SiO)x -Si-O-O-propene]• III) [(SiO)x -Si-O-O-propene]• → (SiO)x -Si-O• + propylene oxide Propylene oxide formation has also been suggested to take place on interstellar ice analogs at 10 K under irradiation 36 or by non-equilibrium reactions considering excited and spinforbidden states started by secondary electrons on ice-coated grains (10 K) 37 .

Computational Details The ORCA software (vs. 3.0.1) 38 was used for all the minimization, potential energy surface (PES) and vibrational frequency analyses using the B3LYP level of theory 39,40 coupled to the atom-pairwise dispersion correction energy with the Becke-Johnson damping 41,42 . To speed up calculations the RI (Resolution of the Identity) 43 and RIJCOSX 44 algorithms were used. For all atoms the split valence basis set SVP derived from the Ahlrichs Valence double-ζ VDZ 45 was used adding d polarization functions on all heavy atoms and p polarization functions on hydrogens. The Ahlrichs polarization functions were obtained from the TurboMole basis set library 46 . Final energies were calculated by using the SVP optimized structures

5



and running single point calculations adopting the triple-ζ basis set TZVP 45,47 adding d polarization functions on all heavy atoms and p polarization functions on hydrogens. MP2 energies were computed using the explicitly correlated MP2-F12 method 48,49 within the Molpro2012.1 software package 50,51 . The energies were obtained as single points from the B3LYP-D3BJ/SVP geometry optimizations described above. The orbital basis sets used were the standard triple-ζ correlation consistent basis sets (cc-pVTZ) 52 For silicon atoms, an additional tight d function was added, [cc-pV(T+d)Z] 53,54 . For density fitting (DF) of Fock and exchange matrices, auxiliary basis sets (ABSs) were used: aug-cc-pVTZ/JKFIT sets for Si, O, and H atoms 55 . For the computation of the MP2-F12 correlation energies, DF sets used the aug-cc-pVTZ/MP2FIT basis sets 55,56 while the complementary auxiliary basis sets (CABS) 57 used for the resolution of the identity (RI) approximation were augcc-pVTZ/OptRI for the Si, O, and H atoms 58 . All MP2-F12 computations included the CABS singles correction to the RHF/ROHF energies 48,49 . A geminal exponent of 1.0 was used throughout. Smaller orbital/auxiliary basis sets are used in the MP2-F12 computations compared to a previous publication by our group 9 . Re-examining thermodynamics of the POSS-H2 catalysis with the smaller basis sets used in this study provided relative energies within 0.2 kcal/mol on average of those found in Ref. 9 , with min/max deviations ranging from -2.3 to +2.0 kcal/mol.

Results and Discussion In Figure 2 the calculated Free Energies of reactions I, II and III are shown,while in Table 1 the single enthalpic and entrop ic terms are reported. Analyzing Figure 2 and Table 1, four salient results will be discussed: the strong thermodynamic force driving the overall reaction and single reaction steps, the barrier-less formation of the peroxo group, the extremely low activation energy for the first peroxo-propene intermediate (1.0 kcal/mol and 0.9 kcal/mol for the B3LYP and MP2-F12 level of theory,

6


Page 6 of 22

Page 7 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2: Calculated ∆G (kcal/mol, T=30 K, spin state: S=1/2; level of theory: black=B3LYP-D3, gray=MP2-F12) for the propylene oxide (PrO) formation in the gas phase via propene (Pr) and a peroxo group. Oxygen in the triplet state: O(3 P). Table 1: ∆H and T∆S contributions to the ∆G term for each single reaction step. MP2-F12 terms in dark gray. Energies in kcal/mol; T=30 K. T∆S terms are derived from the DFT level of theory. Level of Theory DFT/MP2-F12 DFT/MP2-F12 DFT/MP2-F12 DFT/MP2-F12 DFT/MP2-F12a DFT/MP2-F12b a Propylene oxide

Reaction I → II II → TS-I TS-I → III III → TS-II TS-II → I TS-II → I in gas-phase b

∆H T∆S ∆G -60.5/-66.1 -0.6/-0.6 -59.9/-65.5 -60.7/-66.3 -1.7/-1.7 -58.9/-64.6 -70.1/-84.8 -1.8/-1.8 -68.4/-83.0 -64.7/-75.8 -1.8/-1.8 -62.9/-74.0 -79.1/-95.8 -0.5/-0.5 -78.6/-95.3 -87.4/-103.1 -1.7/-1.7 -85.6/-101.4 Propylene oxide adsorbed on catalyst

respectively) and the low kinetic barrier (5.5 and 9.0 kcal/mol for the B3LYP and MP2-F12 level of theory, respectively) for the last ring opening/product formation step. The final product propylene oxide, being a hydrogen bond acceptor, has the possibility to bond to one of the vicinal Si-OH (see Figure S2 in Supp. Info.) resulting in a ∆GAdsorbed−GasP hase =7.0 and 6.1 kcal/mol (DFT and MP2-F12 level of theory, respectively; see Table 1). Initially, the MP2-F12 computation of TS-I showed a "negative" activation energy. This was recognized as an artifact of the composite method (MP2-F12 single points on the B3LYP-

7



D3BJ/SVP optimized geometry). Previous work by one of the authors 59 has shown that the quality of the composite TS energy can be very geometry dependent for early/late transition states. Re-optimizing TS-I at the B3LYP-D3BJ/TZVP level of theory provided little change to the TS-I geometry. However, the improved DFT TS geometry used to calculate TS-I free energy is less "downhill" towards product side, resulting in a change of +5.5 kcal/mol to the TS-I free energy. The reported activation free energy for TS-I with MP2-F12 at the B3LYP TZVP geometry in Figure 2 is now in excellent agreement with the DFT computations. The computed free energies of activation for TS-II at 5.5 (DFT) and 9.0 kcal/mol (MP2F12) may suggest insurmountably slow kinetics at ≈10 K. No lower energy conformations of TS-II could be found. The hydrogen bond between the SiOH and the O-O, firmly aligns O-O orbitals with the orbitals of propene (see below). However, it can be reasonably speculated that locally increased thermal energies due to previous exothermic processes will "heat up" the reactive center. Primarily because TS-I is effectively barrierless yet rate limiting, and propene addition is exothermic, the surface-substrate complex should have enough thermal kinetic energy (even at 10K) to surmount the barrier of TS-II, i.e., due to overall exothermicity of the entire proposed mechanism. The surface absorption of heat would not "trap" the intermediate between TS-I and TS-II due to the minuscule geometric rearrangement necessary to go from the first intermediate to TS-II. Furthermore due to Hammond‘s postulate, TS-II has to more closely resemble the intermediate (III) than TS-I does. In Figure 3 the 3D-models of TS-I, III, and TS-II are reported where except for motion in the -CHCH3 group, there is almost no structural difference between the intermediate III and TS-II. Moreover, with the involvement of radical species a possible spin crossover between the S=1/2 and the S=3/2 surfaces was analyzed to check the existence of low energy intersections allowing an “easy” path to the reaction products. ∆∆GS=3/2−1/2 123.4, 55.7 and 33.4 kcal/mol between the starting compound (I) and each of the two following intermediates (II, III) was computed. Thus, no thermal spin crossover is expected. The overall reaction could also be promoted by small grain (≈0.02 µm) temperature fluctuations, though this

8


Page 8 of 22

Page 9 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3: 3D-models of TS-I, intermediate III and TS-II requires photon absorption 60–62 . Nonetheless, thermal production of propylene oxide in our model can be rationalized despite the lack of fundamental understanding of ISM dust/grain chemistry, even in the absence of transition metals. Interestingly, both transition states (peroxo attack on the C=C bond and ring opening) show a structure similar to the classic butterfly-TS involved in the reaction between a peroxy acid and an alkene to form peroxides (Prilezhaev epoxidation 63 ) i.e. R-C(O)3 H + (R1,2 )C=C(R3,4 ) → RC(O)2 H + C2 (R1,2,3,4 )O. In the butterfly-TS the internal hydrogen bond optimally aligns the peroxo σ orbital to the C=C π double bond orbital allowing the reaction to proceed faster 63,64 , while in the silsesquioxane case the hydrogen bond with the peroxo group is externally donated by a vicinal -SiOH group (Figure 4). The proposed reaction scheme is a “modified” version of the Prilezhaev epoxidation working via a silyl peroxide 65 . Absence of a vicinal silanol on the surface would imply slower kinetics from non-optimal orientation between the C=C and silyl-peroxo group. It should be noted that in industrial catalysis, propene oxidation to propylene oxide is nowadays (partially) performed by the environmentally friendly HPPO (Hydrogen Peroxide Propylene Oxide) process with general stoichiometry: H3 C-CH=CH2 +H2 O2 → CH3 CHCH2 O + H2 O, and is catalyzed by (crystalline) titanium silicalite-1 (TS-1) 66 . Our transition metalfree model indicates that the presence of atomic oxygen allows a direct attack to a surface oxygen with a free valency. As a consequence, the peroxide group exists as a start-up radical via abundant radiation sources in the ISM. 9



Figure 4: TS geometry of the butterfly-mechanism (upper panel) and of the silsesquioxaneperoxo-propene adduct (lower panel) As previously discussed, depending on the irradiation intensity, wavelength, temperature, and particle bombardment, a silica surface and/or bulk is chemically and physically modified 17–19,30,67 transforming surface/bulk atoms into very reactive centers 19,31,68 . Because of the possibility in the peroxo group formation under different charged states, the same silsesquioxane model with an overall positive charge was considered: [(SiO)x -Si-O]+ . Differing from the silsesquioxane model with radical character, the addition of one oxygen (to the free oxygen) results in the formation of an O2 molecule: a) [(SiO)x -Si-O]+ + O (3 P) → [(SiO)x -Si]+ + 3 O2 This is not a surprising result though it evinces chemical defects that can be chemically “aggressive” enough to attack the surface itself. Based on this outcome, the starting structure (I, before the homolytic cleavage of one of the -OH groups) with three vicinal -OH i.e. (SiO)x (SiOH)3 was reanalyzed in the neutral, cationic, and anionic forms using DFT (see Supp. Info.). While in the neutral form a ring of three hydrogen bonds is formed by the three -OH groups, the cationic form loses one H+ leaving the radical (SiO)x -Si-O• . This reaction is a possible alternative step toward the radical form instead of H homolytic cleavage from the neutral form: b) [(SiO)x -(SiOH)3 ]+ → [(SiO)x -(SiOH)2 O• ] + H+ In the anionic state, a water molecule is formed, though strongly clamped with its two 10


Page 10 of 22

Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydrogens via hydrogen bonding with the oxygens of the SiO skeleton. The water oxygen is strongly bonded to a Si atom (1.76 Å): c) [(SiO)x -(SiOH)3 ]− → [(SiO)x -(SiOH)(SiO)H2 O]− In conclusion, to obtain a highly reactive peroxo-radical by a [(SiO)x -(SiOH)3 ], the homolytic cleavage of one OH or the ionization of the grain (reaction b) is necessary. The cationic ‘oxygenyl state’ (reaction a) leaves behind a highly reactive but ineffective (for the considered reaction) ‘silylium ion’ 69 , while in the anionic state (reaction c) a stable ‘oxyanion’ is obtained.

Conclusions The proposed model shows how defects induced by radiation/high energy particles on a solid silicate surface can induce/affect the catalytic activity and modify the chemical/physical stability. Being astrochemically relevant, propylene oxide formation was selected as a reaction model and proposed to be formed on catalytic silyl peroxide centers present on a silica surface. The astrochemical implications of the proposed mechanism are: a) in the gas phase, the direct oxidation of the propene double bond H3 C-CH=CH2 + O (3 P) → CH3 CHCH2 O is strongly exothermic [∆G= -78.6 kcal/mol and -95.3 kcal/mol at the B3LYP-D3 and MP2-F12 level of theory, respectively)]. In the heterogeneous catalysis, such a considerable amount of energy can be partitioned through a series of simple synthetic steps (i.e. I: peroxide formation; II: peroxide-propene adduct; III: propylene oxide formation-detachment) and for each step the excess energy can be thermally relaxed through the skeleton of the silica grain; b) all chemical steps are thermodynamically favored with low activation free energies (0.9 and 1.0 kcal/mol at the DFT and MP2-F12 level of theory, respectively) for the peroxide attack on the C=C bond, and 5.5 kcal/mol (9.0 kcal/mol at the MP2-F12 level of theory) for the ring opening/product formation step. The initial barrierless kinetics (peroxide

11



formation) enables the subsequent mechanistic steps to take place in low temperature environments. However, at 10 K the computed free energies of activation for TS-II at 5.5 (DFT) and 13.0 kcal/mol (MP2-F12) may suggest extremely slow kinetics. Excluding thermal spin crossover, it can be reasonably speculated that locally increased thermal energies due to previous exothermic processes will "heat-up" the reactive center. Another possible mechanism able to overcome the TS-II barrier can be invoked by small grain (0.02 µm) temperature fluctuations, though photon adsorption is required; c) though in this study only propene was considered, other alkene or carbon double bond containing molecules can be reactive on a silica surface with silyl-peroxo groups exposed. As a consequence of the chemistry (electrophiles undergoing nucleophilic attack from water, alcohols, amines, thiols, hydrides) epoxides can be important players in the increase of astromolecular complexity; d) clues were obtained to understand which defects possess a balanced chemical reactivity i.e. are “aggressive” enough to react with a substrate present on the surface, yet “weak” enough to preserve the surface chemical structure. In our case study, the neutral, radical peroxo does not cannibalize the surface. However, in its cationic form (OO+ ), peroxo promptly attacks the surface, releasing O2 and leaving an oxygen deficient center characterized by a silylium ion. Furthermore, the [(SiO)x -(SiOH)3 ] starting structure was analyzed in its neutral, cationic, and anionic form. With a silica surface in the cationic form, a H+ is expelled resulting in the radical [(SiO)x -(SiOH)2 O• ]. Like in direct homolytic cleavage, the hydrogen follows a different dissociation path. In the anionic form of the silica skeleton, a water molecule is strongly bound. In the neutral form of the amorphous silica surface, a ring of hydrogen bonds between the vicinal -OH is observed. The chemistry reported here has implications on understanding how processing phases (T, radiation and particle bombardment) affect the nature of the reactive groups on a silica surface leading to surface modifications influencing and/or changing the silica surface catalytic activity; e) from the computational point of view, the B3LYP-D3 results compare well with those ob-

12


Page 12 of 22

Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


tained at the MP2-F12 level of theory. The MP2-F12 results provide increased exothermicity for the elementary steps of the catalysis. General agreement between DFT and MP2-F12 sets a consistent and robust protocol for future thermochemical and kinetic astrochemical modeling; f ) finally, the propylene oxide formation through the gas-solid heterogeneous catalysis of silica surfaces shows how complex organic matter in space can be potentially synthesized through a "fine chemistry process" by the use of main group elements with free valences even without the involvement of transition metals, which in general are even more prone to perform complex catalytic reactions.

Acknowledgement We thank the Department of Chemistry at the University of Memphis, the University of Memphis High Performance Computing Facility, and CROMIUM (Computational Research on Materials Institute at the University of Memphis) for support.

References (1) McGuire, B. A.; Carrol, P. B.; Loomis, R. A.; Finneran, I. A.; Jewell, P. R.; Remijan, A. J.; Blake, G. A. Discovery of the Interstellar Chiral Molecule Propylene Oxide (CH3 CHCH2 O). Science 2016, 352, 1449–1452. (2) Pizzarello, S.; Huang, Y.; Alexandre, M. R. Molecular Asymmetry in Extraterrestrial Chemistry: Insights from a Pristine Meteorite. Proc. Nat. Acad. Sci. USA 2008, 105, 3700–3704. (3) Pizzarello, S.; Schrader, D. L.; Monroe, A. A.; Lauretta, D. S. Large Enantiomeric Excesses in Primitive Meteorites and the Diverse Effects of Water in Cosmochemical Evolution. Proc. Nat. Acad. Sci. USA 2012, 109, 11949–11954. 13



(4) Pizzarello, S.; Davidowski, S. K.; Holland, G. P.; Williams, L. B. Processing of Meteoritic Organic Materials as a Possible Analog of Early Molecular Evolution in Planetary Environments. Proc. Nat. Acad. Sci. USA 2013, 110, 15614–15619. (5) Altwegg, K.; Balsiger, H.; Bar-Nun, A.; Berthelier, J.-J.; Bieler, A.; Bochsler, P.; Briois, C.; Calmonte, U.; Combi, M. R.; Cottin, H. et al. Prebiotic Chemicals-Amino Acid and Phosphorus-in the Coma of Comet 67P/Churyumov-Gerasimenko. Sci. Adv. 2016, 2, e1600285. (6) Jones, A. P. Dust Evolution, a Global View: III. Core/Mantle Grains, Organic NanoGlobules, Comets and Surface Chemistry. R. Soc. Open Sci. 2016, 3, 160224. (7) Herbst, E. Three Milieux for Interstellar Chemistry: Gas, Dust, and Ice. Phys. Chem. Chem. Phys. 2014, 16, 3344–3359. (8) Henning, T. Cosmic Silicates. Annu. Rev. Astron. Astrophys. 2010, 48, 21–46. (9) Fioroni, M.; DeYonker, N. J. H2 Formation on Cosmic Grain Siliceous Surfaces Grafted with Fe+ : a Silsesquioxanes Based Computational Model. Chem. Phys. Chem. 2016, 17, 3390–3394. (10) Cuppen, H. M.; Walsh, C.; Lamberts, T.; Semenov, D.; Garrod, R. T.; Penteado, E. M.; Ioppolo, S. Grain Surface Models and Data for Astrochemistry. Space Sci. Rev. 2017, 212, 1–58. (11) Kemper, F.; Vriend, W. J.; Tielens, A. G. G. M. The Absence of Crystalline Silicates in the Diffuse Interstellar Medium. Astrophys. J. 2004, 609, 826–837. (12) Li, M. P.; Zhao, G.; Li, A. On the Crystallinity of Silicate Dust in the Interstellar Medium. Mon. Not. R. Astron. Soc. Lett. 2007, 382, L26–L29. (13) Li, A.; Draine, B. T. On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium. Astrophys. J. Lett. 2001, 550, L213–L217. 14


Page 14 of 22

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) He, J.; Jing, D.; Vidali, G. Atomic Oxygen Diffusion on and Desorption from Amorphous Silicate Surfaces. Phys. Chem. Chem. Phys. 2014, 16, 3493–3500. (15) Jing, D.; He, J.; Brucato, J. R.; Vidali, G.; Tozzetti, L.; Sio, A. D. Formation of Molecular Oxygen and Ozone on Amorphous Silicates. Astrophys. J. 2012, 756, 98. (16) Jing, D.; He, J.; Bonini, M.; Brucato, J. R.; Vidali, G. Sputtering Effects and Water Formation on an Amorphous Silicate Surface. J. Phys. Chem. A 2013, 117, 3009–3016. (17) Nalwa, H. S., Ed. Silicon-Based Materials and Devices; Academic Press, San Diego, Calif, USA, 2001. (18) Shi-Zhen, X.; Hai-Bing, L.; Xiao-Dong, Y.; Jin, H.; Xiao-Dong, J.; Hai-Jun, W.; XiaoTao, Z.; Wan-Guo, Z. Effects of Vacuum on Fused Silica UV Damage. Chinese Phys. Lett. 2008, 25, 223–226. (19) Pacchioni, G., Skuja, L., Griscom, D., Eds. Defects in SiO2 and Related Dielectrics: Science and Technology; NATO Science Series II. Mathematics, Physics and Chemistry; Springer Science+Business Media, B.V., 2000; Vol. 2. (20) Sargent, B. A.; Forrest, W. J.; Tayrien, C.; McClure, M. K.; Li, A.; Basu, A. R.; Manoj, P.; Watson, D. M.; Bohac, C. J.; Furlan, E. et al. Silica in Protoplanetary Disks. Astrophys. J. 2009, 690, 1193–1207. (21) Thomas, J. M.; Raja, R.; Lewis, D. W. Single-Site Heterogeneous Catalysts. Angew. Che. Int. Ed. 2005, 44, 6456–6482. (22) Kerkeni, B.; Bacchus-Montabonel, M.-C.; Bromley, S. T. How Hydroxylation Affects Hydrogen Adsorption and Formation on Nanosilicates. Mol. Astrophys. 2017, 7, 1–8. (23) Goumans, T. P. M.; Wander, A.; Catlow, R. A.; Brown, W. A. Silica Grain Catalysis of Methanol Formation. Mon. Not. R. Astron. Soc. 2007, 382, 1829–1832.

15



(24) Rimoldi, M.; Mezzetti, A. Site Isolated Complexes of Late Transition Metals Grafted on Silica: Challenges and Chances for Synthesis and Catalysis. Catal. Sci. Technol. 2014, 4, 2724–2740. (25) Zhuralev, L. T. The Surface Chemistry of Amorphous Silica. Zhuravlev Model. Coll. Surf. A 2000, 173, 1–38. (26) Bromley, S. T.; Goumans, T. P. M.; Herbst, E.; Jones, A. P.; Slater, B. Challenges in Modelling the Reaction Chemistry of Interstellar Dust. Phys. Chem. Chem. Phys. 2014, 16, 18263–18643. (27) Jones, A. P. In Astrophysics of Dust; Witt, A. N., Clayton, G. C., Draine, B. T., Eds.; Astron. Soc. Pac. Conf. Ser., 2004; Vol. 309; p 347. (28) Goumans, T. P. M.; Catlow, R. A.; Brown, W. A. Catalysis of Addition Reactions by a Negatively Charged Silica Surface Site on a Dust Grain. J. Phys. Chem. C 2008, 112, 15419–15422. (29) Meana-Pan˜eda, R.; Paukku, Y.; Duanmu, K.; Norman, P.; Schwartzentruber, T. E.; Truhlar, D. G. Atomic Oxygen Recombination at Surface Defects on Reconstructed (0001) α - Quartz Exposed to Atomic and Molecular Oxygen. J. Phys. Chem. C 2015, 119, 9287–9301. (30) Devine, R. A. B., Duraud, J. P., Dooryhée, E., Eds. Structure and Imperfections in Amorphous and Crystalline Silicon Dioxide; John Wiley and Sons, Chichester, UK, 2000. (31) Goldsmith, B. R.; Peters, B.; Johnson, J. K.; Gates, B. C.; Scott, S. L. Beyond Ordered Materials: Understanding Catalytic Sites on Amorphous Solids. ACS Catal. 2017, 7, 7543–7557.

16


Page 16 of 22

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(32) Cuppen, H. M.; Herbst, E. Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains. Astrophys. J. 2007, 668, 294–309. (33) Cazaux, S.,; Bossa, J.-B.,; Linnartz, H.,; Tielens, A. G. G. M., Pore Evolution in Interstellar Ice Analogues - Simulating the Effects of Temperature Increase. Astronom. Astrophys. 2015, 573, A16. (34) Cartwright, J. H. E.; Escribano, B.; Sainz-Diaz, C. I. The Mesoscale Morphologies of Ice Films: Porous and Biomorphic Forms of Ice under Astrophysical Conditions. Astrophys. J. 2008, 687, 1406–1414. (35) Marcelino, N.; Cernicharo, J.; Agúndez, M.; Roueff, E.; Martín-Pintado, J.; Mauersberger, R.; Thum, C. Discovery of Interstellar Propylen (CH2 CHCH3 ): Missing Links in Interstellar Gas-Phase Chemistry. Astrophys. J. 2007, 665, L127–L130. (36) Hudson, R. L.; Loeffler, M. J.; Yocum, K. M. Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule. Astrophys. J. 2017, 835, 225. (37) Bergantini, A.; Abplanalp, M. J.; Pokhilko, P.; Krylov, A. I.; Shingledecker, C. N.; Herbst, E.; Kaiser, R. I. A Combined Experimental and Theoretical Study on the Formation of Interstellar Propylene Oxide (CH3 CHCH2 O) A Chiral Molecule. Astrophys. J. 2018, 860, 108. (38) Neese, F. The ORCA Program System. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2, 73–78. (39) Becke, A. D. Density Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652. (40) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab Initio Calculation

17



of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 1994, 98, 11623–11627. (41) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping Function in Dispersion Corrected Density Functional Theory. J. Comput. Chem. 2011, 32, 1456–1465. (42) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab-Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132, 154104. (43) Neese, F. An Improvement of the Resolution of the Identity Approximation for the Calculation of the Coulomb Matrix. J. Comp. Chem. 2003, 24, 1740–1747. (44) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient, Approximate and Parallel Hartree-Fock and Hybrid DFT Calculations. A "Chain-of-Spheres" Algorithm for the Hartree-Fock Exchange. Chem. Phys. 2009, 356, 98–109. (45) Schaefer, A.; Horn, H.; Ahlrichs, R. Fully Optimized Contracted Gaussian Basis Sets for Atoms Li to Kr. J. Chem. Phys. 1992, 97, 2571–2577. (46) ftp.chemie.uni-karlsruhe.de/pub/basen. (47) Schaefer, A.; Huber, C.; Ahlrichs, R. Fully Optimized Contracted Gaussian-Basis Sets of Triple Zeta Valence Quality for Atoms Li to Kr. J. Chem. Phys. 1994, 100, 5829– 5835. (48) Knizia, G.; Werner, H. J. Explicitly Correlated RMP2 for High-Spin Open-Shell Reference States. J. Chem. Phys. 2008, 128, 154103. (49) Werner, H. J.; Adler, T. B.; Manby, F. R. General Orbital Invariant MP2-F12 Theory. J. Chem. Phys. 2007, 126, 164102.

18


Page 18 of 22

Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(50) Werner, H. J.; Knowles, P. J.; Knizia, G.; Manby, F. R.; Schütz, M. P. C.; Györffy, W.; Kats, D.; Korona, T.; Lindh, R.; Mitrushenkov, A. et al. MOLPRO, Version 2012.1, a Package of Ab-Initio Programs. 2012; http://www.molpro.net. (51) Werner, H.-J.; Knowles, P. J.; Knizia, G.; Manby, F. R.; Schütz, M. Molpro: a General Purpose Quantum Chemistry Program Package. WIREs Comput Mol Sci 2012, 2, 242–253. (52) Dunning, T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007–1023. (53) Woon, D. E.; Dunning, T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. III. The Atoms Aluminum through Argon. J. Chem. Phys. 1993, 98, 1358–1371. (54) Dunning, T. H.; Peterson, K. A.; Wilson, A. K. Gaussian Basis Sets for Use in Correlated Molecular Calculations. X. The Atoms Aluminum through Argon Revisited. J. Chem. Phys. 2001, 114, 9244–9253. (55) Weigend, F.; Köhn, A.; Hättig, C. Efficient Use of the Correlation Consistent Basis Sets in Resolution of the Identity MP2 Calculations. J. Chem. Phys. 2002, 116, 3175–3183. (56) Hill, J. G.; Platts, J. A. Auxiliary Basis Sets for Density Fitting-MP2 Calculations: Nonrelativistic Triple-ζ All-Electron Correlation Consistent Basis Sets for the 3d Elements Sc-Zn. J. Chem. Phys. 2008, 128, 044104. (57) Valeev, E. F. Improving on the Resolution of the Identity in Linear {R12} ab initio Theories. Chem. Phys. Lett. 2004, 395, 190–195. (58) Yousaf, K. E.; Peterson, A., Kirk Optimized Complementary Auxiliary Basis Sets for Explicitly Correlated Methods: aug-cc-pVnZ Orbital Basis Sets. Chem. Phys. Lett. 2009, 476, 303–307. 19



(59) Grimes, T. V.; Wilson, A. K.; DeYonker, N. J.; Cundari, T. R. Performance of the Correlation Consistent Composite Approach for Transition States: A Comparison to G3B Theory. J. Chem. Phys. 2007, 127, 154117. (60) Aannestad, S. J., Per A.and Kenyon Temperature Fluctuations in Interstellar Dust Grains. Astrophys. Space Sci. 1979, 65, 155–166. (61) Kobi, H.; Perets, H. B.; Biham, O. Temperature Fluctuations of Interstellar Dust Grains. arXiv:0709.3198 2007, (62) Chen, L.-F.; Chang, Q.; Xi, H.-W. Effect of Stochastic Grain Heating on Cold Dense Clouds Chemistry. Mon. Not. R. Astron. Soc. 2018, 479, 2988–3001. (63) Edwards, J. O. Peroxide Reaction Mechanisms; Interscience, New York, 1962; pp 67– 106. (64) Mello, R.; Alcalde-Aragonés, A.; González Núñez, M. E.; Asensio, G. Epoxidation of Olefins with a Silica-Supported Peracid. J. Org. Chem. 2012, 77, 6409–6413. (65) Estévez, C. M.; Dmitrenko, O.; Winter, J. E.; Bach, R. D. Reactivity of Alkyl versus Silyl Peroxides. The Consequences of 1,2-Silicon Bridging on the Epoxidation of Alkenes with Silyl Hydroperoxides and Bis(trialkylsilyl)peroxides. J. Org. Chem. 2000, 65, 8629–8639. (66) Russo, V.; Tesser, R.; Di Serio, M. Chemical and Technical Aspects of Propene Oxide Production via Hydrogen Peroxide (HPPO Process). Ind. Eng. Chem. Res. 2013, 52, 1168–1178. (67) Buscarino, G.; Agnello, S.; Gelardi, M. F.; Boscaino, R. The Role of Impurities in the Irradiation Induced Densification of Amorphous SiO2 . J. Phys. Condens. Matter 2010, 22, 255403.

20


Page 20 of 22

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(68) Hamid, M. S.; Firmansyah, M. L.; Triwahyono, S.; Jalil, A. A.; Mukti, R. R.; Febriyanti, E.; Suendo, V.; Setiabudi, H. D.; Mohamed, M.; Nabgan, A. Oxygen Vacancy-Rich Mesoporous Silica KCC-1 for CO2 Methanation. Appl. Catal. A 2017, 532, 86–94. (69) Klare, H. F. T.; Oestreich, M. Silylium Ions in Catalysis. Dalton Trans. 2010, 39, 9176–9184.

Supporting Information Available • ORCA input template • XYZ coordinates • Energies • PES

21



Graphical TOC Entry

22


Page 22 of 22

Propylene Oxide Formation on a Silica Surface with Peroxo Defects

Recommend Documents