1
|
Bruckhoff T, Ballmann J, Gade LH. Radicalizing CO by Mononuclear Palladium(I). Angew Chem Int Ed Engl 2024; 63:e202320064. [PMID: 38498121 DOI: 10.1002/anie.202320064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 03/06/2024] [Accepted: 03/12/2024] [Indexed: 03/20/2024]
Abstract
A mononuclear, T-shaped palladium(I) d9 metalloradical (3), stabilized by a bulky carbazole-based PNP-ligand, was obtained by reduction of palladium chloride or thermal Pd-C bond homolysis of the corresponding neopentyl complex. Pressurizing with CO gave the Pd(I) carbonyl complex, which was structurally characterized by X-ray diffraction. Delocalization of the unpaired electron to the carbonyl carbon was detected by EPR spectroscopy and theoretically modeled by DFT and ab initio methods. The partially reduced and radicalized CO slowly reacts with di(tert-butyl) disulfide under homolytic S-S cleavage and C-S bond formation to give the corresponding metallathioester.
Collapse
Affiliation(s)
- Tim Bruckhoff
- Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, 69120, Heidelberg, Germany
| | - Joachim Ballmann
- Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, 69120, Heidelberg, Germany
| | - Lutz H Gade
- Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, 69120, Heidelberg, Germany
| |
Collapse
|
2
|
Westawker LP, Khusnutdinova JK, Wallick RF, Mirica LM. Palladium K-edge X-ray Absorption Spectroscopy Studies on Controlled Ligand Systems. Inorg Chem 2023; 62:21128-21137. [PMID: 38039413 DOI: 10.1021/acs.inorgchem.3c03032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2023]
Abstract
X-ray absorption spectroscopy (XAS) is widely used across the life and physical sciences to identify the electronic properties and structure surrounding a specific element. XAS is less often used for the characterization of organometallic compounds, especially for sensitive and highly reactive species. In this study, we used solid- and solution-phase XAS to compare a series of 25 palladium complexes in controlled ligand environments. The compounds include palladium centers in the formal I, II, III, and IV oxidation states, supported by tridentate and tetradentate macrocyclic ligands, with different halide and methyl ligand combinations. The Pd K-edge energies increased not only upon oxidizing the metal center but also upon increasing the denticity of the ligand framework, substituting sigma-donating methyl groups with chlorides, and increasing the charge of the overall metal complex by replacing charged ligands with neutral ligands. These trends were then applied to characterize compounds whose oxidation states were otherwise unconfirmed.
Collapse
Affiliation(s)
- Luke P Westawker
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois 61801, United States
| | - Julia K Khusnutdinova
- Coordination Chemistry and Catalysis Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan
| | - Rachel F Wallick
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois 61801, United States
| | - Liviu M Mirica
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, Illinois 61801, United States
| |
Collapse
|
3
|
Chakrabarti S, Woods TJ, Mirica LM. Insights into the Mechanism of CO 2 Electroreduction by Molecular Palladium-Pyridinophane Complexes. Inorg Chem 2023; 62:16801-16809. [PMID: 37787756 DOI: 10.1021/acs.inorgchem.3c02236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Herein, we report the synthesis, characterization, and electrocatalytic CO2 reduction activity of a series of Pd(II) complexes supported by tetradentate pyridinophane ligands. In particular, we focus on the electrocatalytic CO2 reduction activity of a Pd(II) complex supported by the mixed hard--soft donor ligand 2,11-dithia[3.3](2,6)pyridinophane (N2S2). We also provide spectroscopic evidence of a CO-induced decomposition pathway for the same catalyst, which provides insights into catalyst poisoning for molecular Pd CO2 reduction electrocatalysts.
Collapse
Affiliation(s)
- Sagnik Chakrabarti
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Toby J Woods
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Liviu M Mirica
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| |
Collapse
|
4
|
Singh S, Shinde VN, Kumar S, Meena N, Bhuvanesh N, Rangan K, Kumar A, Joshi H. Mono and Dinuclear Palladium Pincer Complexes of NNSe Ligand as a Catalyst for Decarboxylative Direct C-H Heteroarylation of (Hetero)arenes. Chem Asian J 2023; 18:e202300628. [PMID: 37602812 DOI: 10.1002/asia.202300628] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 08/18/2023] [Accepted: 08/18/2023] [Indexed: 08/22/2023]
Abstract
This report describes the synthesis of a new NNSe pincer ligand and its mono- and dinuclear palladium(II) pincer complexes. In the absence of a base, a dinuclear palladium pincer complex (C1) was isolated, while in the presence of Et3 N base a mononuclear palladium pincer complex (C2) was obtained. The new ligand and complexes were characterized using techniques like 1 H, 13 C{1 H} nuclear magnetic resonance (NMR), fourier transform infrared (FTIR), high-resolution mass spectrometry (HRMS), ultraviolet-visible (UV-Visible), and cyclic voltammetry. Both the complexes showed pincer coordination mode with a distorted square planar geometry. The complex C1 has two pincer ligands attached through a Pd-Pd bond in a dinuclear pincer fashion. The air and moisture-insensitive, thermally robust palladium pincer complexes were used as the catalyst for decarboxylative direct C-H heteroarylation of (hetero)arenes. Among the complexes, dinuclear pincer complex C1 showed better catalytic activity. A variety of (hetero)arenes were successfully activated (43-87 % yield) using only 2.5 mol % of catalyst loading under mild reaction conditions. The PPh3 and Hg poisoning experiments suggested a homogeneous nature of catalysis. A plausible reaction pathway was proposed for the dinuclear palladium pincer complex catalyzed decarboxylative C-H bond activation reaction of (hetero)arenes.
Collapse
Affiliation(s)
- Sohan Singh
- ISC Laboratory, Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer, Rajasthan, 305817, India
| | - Vikki N Shinde
- Department of Chemistry, Birla Institute of Technology and Science, Pilani, Pilani Campus, Pilani, 333031, India
| | - Sunil Kumar
- ISC Laboratory, Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer, Rajasthan, 305817, India
| | - Neha Meena
- Department of Chemistry, Birla Institute of Technology and Science, Pilani, Pilani Campus, Pilani, 333031, India
| | - Nattamai Bhuvanesh
- Department of Chemistry, Texas A&M University, PO Box 30012, College Station, Texas, 77842-3012, USA
| | - Krishnan Rangan
- Department of Chemistry, Birla Institute of Technology and Science Pilani, Hyderabad Campus, Telangana, 500078, India
| | - Anil Kumar
- Department of Chemistry, Birla Institute of Technology and Science, Pilani, Pilani Campus, Pilani, 333031, India
| | - Hemant Joshi
- ISC Laboratory, Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer, Rajasthan, 305817, India
| |
Collapse
|
5
|
Zhao X, Kang S, Zhang H, Yang H, Dou M, Zhao H, Li D, Dou J. Highly efficient binuclear cobalt-bis(4-methylthiosemicarbazone) complex co-catalyst to support Cd0.5Zn0.5S NPs for enhanced photocatalytic hydrogen evolution. Inorganica Chim Acta 2023. [DOI: 10.1016/j.ica.2023.121497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
|
6
|
Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst. Nat Commun 2023; 14:905. [PMID: 36807358 PMCID: PMC9938211 DOI: 10.1038/s41467-023-36609-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 02/06/2023] [Indexed: 02/19/2023] Open
Abstract
Significant progress has been made in the bioinorganic modeling of the paramagnetic states believed to be involved in the hydrogen redox chemistry catalyzed by [NiFe] hydrogenase. However, the characterization and isolation of intermediates involved in mononuclear Ni electrocatalysts which are reported to operate through a NiI/III cycle have largely remained elusive. Herein, we report a NiII complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for the hydrogen evolution reaction (HER) with turnover frequencies of ~3,000 s-1 and a overpotential of 670 mV in the presence of trifluoroacetic acid. This electrocatalyst follows a hitherto unobserved HER mechanism involving C-H activation, which manifests as an inverse kinetic isotope effect for the overall hydrogen evolution reaction, and NiI/NiIII intermediates, which have been characterized by EPR spectroscopy. We further validate the possibility of the involvement of NiIII intermediates by the independent synthesis and characterization of organometallic NiIII complexes.
Collapse
|
7
|
Tran GN, Bouley BS, Mirica LM. Isolation and Characterization of Heteroleptic Mononuclear Palladium(I) Complexes. J Am Chem Soc 2022; 144:20008-20015. [PMID: 36257056 DOI: 10.1021/jacs.2c08765] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Catalytic transformations involving Pd(0)/Pd(II) catalytic cycles are very well known, and processes involving high-valent Pd(III) and Pd(IV) and low-valent Pd(I) intermediates have also gained interest in recent years. Although low-valent Pd(I) intermediates are proposed in these catalytic cycles, isolated and characterized mononuclear Pd(I) species are very rare. Herein, we report the isolation of two heteroleptic mononuclear Pd(I) complexes stabilized by dithiapyridinophane ligands that were fully characterized by single-crystal X-ray diffraction; EPR, IR, UV-vis spectroscopies; and computational studies. Excitingly, one of these Pd(I) complexes shows Kumada Csp3-Csp2 cross-coupling competency, and initial studies of the other shows direct evidence for Csp3-H bond activation proposed to occur at the Pd(I) center.
Collapse
Affiliation(s)
- Giang N Tran
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Bailey S Bouley
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Liviu M Mirica
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| |
Collapse
|
8
|
Dinh HM, Gridneva T, Karimata A, Garcia-Roca A, Pruchyathamkorn J, Patil PH, Petrov A, Sarbajna A, Lapointe S, Khaskin E, Fayzullin RR, Khusnutdinova JR. Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes. Dalton Trans 2022; 51:14734-14746. [PMID: 36106442 DOI: 10.1039/d2dt02219b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2-S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration.
Collapse
Affiliation(s)
- Hoan Minh Dinh
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Tatiana Gridneva
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Ayumu Karimata
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Alèria Garcia-Roca
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Jiratheep Pruchyathamkorn
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Pradnya H Patil
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Andrey Petrov
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Abir Sarbajna
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Sébastien Lapointe
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Eugene Khaskin
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| | - Robert R Fayzullin
- Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences, 8 Arbuzov Street, Kazan 420088, Russian Federation
| | - Julia R Khusnutdinova
- Okinawa Institute of Science and Technology Graduate University, Coordination Chemistry and Catalysis Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
| |
Collapse
|
9
|
Sinclair MJG, Chaplin AB. Heterolytic carbon-iodine bond cleavage by a palladium(I) metalloradical. Dalton Trans 2022; 51:11617-11619. [PMID: 35852934 DOI: 10.1039/d2dt02152h] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The well-defined Pd(I) metalloradical [Pd(PtBu3)2]+ reacts with aryl and alkyl iodides at room temperature, yielding [Pd(PtBu3)(μ-I)]2 and phosphonium salts. Pd(II) aryl/alkyl derivates, reflecting net radical oxidative addition of the substrate to the metalloradical, are generated during the reaction and two examples have been isolated and crystallographically characterised.
Collapse
Affiliation(s)
- Matthew J G Sinclair
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
| | - Adrian B Chaplin
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
| |
Collapse
|
10
|
Hayton TW, Shafaat HS. Periodic TableTalks: An Oasis of Science within a Conference Desert. Inorg Chem 2022; 61:5965-5971. [DOI: 10.1021/acs.inorgchem.2c01108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Trevor W. Hayton
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Hannah S. Shafaat
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| |
Collapse
|
11
|
Sinha S, Tran GN, Na H, Mirica LM. Electrocatalytic H 2 evolution promoted by a bioinspired (N2S2)Ni(II) complex. Chem Commun (Camb) 2022; 58:1143-1146. [PMID: 34981080 DOI: 10.1039/d1cc05139c] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A bioinspired (N2S2)Ni(II) electrocatalyst is reported that produces H2 from CF3CO2H with a turnover frequency (TOF) of ∼1250 s-1 at low acid concentration (<0.043 M) in MeCN. A mechanism for the H2 production by this electrocatalyst is proposed and its activity is benchmarked against those of other reported molecular Ni H2 evolution electrocatalysts. The involvement of a hemilabile pyridyl group of the N2S2 ligand is proposed to mimic the role of a cysteine residue involved in the biological proton reduction performed by [NiFe] hydrogenases.
Collapse
Affiliation(s)
- Soumalya Sinha
- Department of Chemistry University of Illinois at Urbana Champaign 600 S. Mathews Avenue, Urbana, Illinois 61801, USA.
| | - Giang N Tran
- Department of Chemistry University of Illinois at Urbana Champaign 600 S. Mathews Avenue, Urbana, Illinois 61801, USA.
| | - Hanah Na
- Department of Chemistry University of Illinois at Urbana Champaign 600 S. Mathews Avenue, Urbana, Illinois 61801, USA.
| | - Liviu M Mirica
- Department of Chemistry University of Illinois at Urbana Champaign 600 S. Mathews Avenue, Urbana, Illinois 61801, USA.
| |
Collapse
|
12
|
Liu J, Bollmeyer MM, Kim Y, Xiao D, MacMillan SN, Chen Q, Leng X, Kim SH, Zhao L, Lancaster KM, Deng L. An Isolable Mononuclear Palladium(I) Amido Complex. J Am Chem Soc 2021; 143:10751-10759. [PMID: 34232039 DOI: 10.1021/jacs.1c04965] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mononuclear Pd(I) species are putative intermediates in Pd-catalyzed reactions, but our knowledge about them is limited due to difficulties in accessing them. Herein, we report the isolation of a Pd(I) amido complex, [(BINAP)Pd(NHArTrip)] (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene, ArTrip = 2,6-bis(2',4',6'-triisopropylphenyl)phenyl), from the reaction of (BINAP)PdCl2 with LiNHArTrip. This Pd(I) amido species has been characterized by X-ray crystallography, electron paramagnetic resonance, and multiedge Pd X-ray absorption spectroscopy. Theoretical study revealed that, while the three-electron-two-center π-interaction between Pd and N in the Pd(I) complex imposes severe Pauli repulsion in its Pd-N bond, pronounced attractive interligand dispersion force aids its stabilization. In accord with its electronic features, reactions of homolytic Pd-N bond cleavage and deprotonation of primary amines are observed on the Pd(I) amido complex.
Collapse
Affiliation(s)
- Jian Liu
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Melissa M Bollmeyer
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Yujeong Kim
- Western Seoul Center, Korea Basic Science Institute (KBSI), Seoul 03759, Republic of Korea.,Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Republic of Korea
| | - Dengmengfei Xiao
- Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816, China
| | - Samantha N MacMillan
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Qi Chen
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Xuebing Leng
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Sun Hee Kim
- Western Seoul Center, Korea Basic Science Institute (KBSI), Seoul 03759, Republic of Korea.,Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Republic of Korea
| | - Lili Zhao
- Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816, China
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Liang Deng
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| |
Collapse
|
13
|
Van der Mynsbrugge J, Head-Gordon M, Bell AT. Computational Modeling Predicts the Stability of Both Pd + and Pd 2+ Ion-Exchanged into H-CHA. JOURNAL OF MATERIALS CHEMISTRY. A 2021; 9:2161-2174. [PMID: 33686355 PMCID: PMC7936627 DOI: 10.1039/d0ta11254b] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Passive NOx adsorbers (PNA) using Pd/zeolites have emerged as a promising solution for the reduction of cold-start emissions from vehicle exhaust. However, the nature of the active sites and the mechanisms underlying NOx adsorption in Pd/zeolites remain a subject of ongoing investigation. In this study, we employ quantum chemical simulations to investigate the structure of Pd species in cation-exchange sites at isolated Al and Al pairs in the 6-ring and 8-ring of the CHA framework, before the introduction of NOx. Our calculations show that the speciation of Pd in these exchange sites strongly depends on the precise Al arrangement within the framework, as well as the operating conditions. Ionically dispersed Pd is found to be the most favorable species over a wide range of oxidizing and reducing conditions. Small oligomers of PdO and metallic Pd do not appear to be competitive at either isolated Al or Al pairs. Notably, our calculations show that ion exchange sites other than next-next-nearest neighbor Al pairs in the 6-ring will be preferentially occupied by Pd+ instead of Pd2+. The stability of Pd+ in the zeolite environment is an interesting contrast with its rareness in molecular Pd compounds. Nonetheless, a detailed analysis of the electronic structure shows that predicted Pd oxidation states are consistent with chemical intuition for all complexes investigated in this study. We also discuss the potential ambiguity in Pd characterization provided by typical experimental techniques such as XANES, EXAFS and UV-VIS, and highlight the need for additional EPR spectroscopy studies to further elucidate the initial Pd speciation in zeolites for PNA applications.
Collapse
Affiliation(s)
- Jeroen Van der Mynsbrugge
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720, USA
| | - Martin Head-Gordon
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | - Alexis T. Bell
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720, USA
| |
Collapse
|