Acidic OH Research Articles

Non-oxidative methane dehydroaromatization on Mo/HZSM-5 catalysts: Tuning the acidic and catalytic properties through partial exchange of zeolite protons with alkali and alkaline-earth cations

In this work, partial exchange of protons in H-ZSM-5 zeolite with alkali (Na+, Cs+) and alkaline-earth (Ca2+, Mg2+) cations was applied as a simple means of modulating the density and strength of the zeolite Brønsted acid sites with the aim of depressing the coke-forming tendency and, hence, of improving the stability of Mo/ZSM-5 catalysts (3wt% Mo, Si/Al=15) for methane dehydroaromatization (MDA). The materials were characterized by ICP-OES, XRD, N2 physisorption, 27Al MAS NMR, H2-TPR, DRS UV–vis, XPS, FTIR-pyridine, and NH3-TPD. Coke in spent catalysts was characterized by TGA and TPO. The MDA experiments lasted about 8h and were performed at the standard conditions of 700°C, 1bar, and GHSV of 1500cm3/(gcath). The preferential neutralization of the most acidic OH groups (likely associated to “isolated Al” atoms in the zeolite framework) by Na+ reduced both the amount and the average strength of the remaining Brønsted acid sites. The reduction in the acid site density decreased the amount of (Mo2O5)2+ and/or (MoO2)2+ species anchored to the zeolite framework (precursors of the active MoCx/MoCxOy nanoclusters) and, consequently, the methane conversion rate. However, an optimum exchange level (corresponding to a Na/Al atomic ratio of 0.1) was found for which the derived catalyst (Mo/Na10HZ5) exhibited an unusually low coke selectivity of ca. 10% (on a C basis) as compared to the selectivity of ca. 36% obtained for the parent Mo/HZ5 catalyst. Concomitantly, the selectivity to benzene raised from 42% for Mo/HZ5 to 66% for Mo/Na10HZ5 and the decay rates for both methane conversion and benzene formation (at TOS>6h) decreased by about one order of magnitude for Mo/Na10HZ5 with respect to Mo/HZ5. The increased benzene selectivity and stability lead to higher and more sustained benzene formation rates during the last reaction stages (TOS>6h) for Mo/Na10HZ5 in spite of its lower activity for methane conversion in comparison to Mo/HZ5. Similar trends, though less pronounced, were observed for the catalyst comprising the zeolite exchanged with Cs+ at the optimum exchange level of M+/Al=0.1. On the other hand, the exchange with divalent Ca2+ and Mg2+ cations (at an equivalent exchange level of M2+/Al=0.05) produced zeolites having similar amount of Brønsted acid sites but with a higher average strength than those of the zeolites exchanged with Na+ and Cs+. Despite an alike density of Brønsted acid sites, the migration of Mo and formation of exchanged divalent Mo cationic precursors within the zeolite channels were restrained in the catalysts comprising the Ca2+ and Mg2+ exchanged zeolites as part of the sites required to accommodate the (Mo2O5)2+/(MoO2)2+ species (those associated to the so-called “Al pairs”) were already balanced by the alkaline-earth cations. Consequently, lower methane conversion rates were obtained for the Mo/Ca5HZ5 and Mo/Mg5HZ5 catalysts. In turn, the reduction in Brønsted acidity upon partial exchange with Ca2+ and Mg2+ also decreased the selectivity to coke and increased that to benzene of the corresponding catalysts with respect to the reference Mo/HZ5 sample, though the changes were much less notorious than for the catalysts based on the zeolites exchanged with alkali cations. However, differently from the later, the reduction in coke selectivity did not translate into an enhanced stability of the Mo/Ca5HZ5 and Mo/Mg5HZ5 catalysts with respect to Mo/HZ5 which, according to TPO, was ascribed to the more inert nature (higher deactivating power) of their carbon deposits.

Enhanced metathesis activity of low loading Re2O7/Al2O3 catalysts for propylene production by using aluminum nitrate as Al2O3 precursor

A series of alumina supported Re2O7 catalysts (4wt% Re loading) were prepared by using aluminium nitrate (ANN) calcined at different temperatures (400, 550, and 750°C) as the supports and impregnated with ammonium perrhenate solution. Despite their lower pore volume and smaller average pore size, the catalyst performances in the metathesis of ethylene and 2-pentene in terms of 2-pentene conversion and propylene selectivity of all the Re2O7/ANN were much improved as compared to the commercial γ-Al2O3 supported one (Re2O7/Al-com) with the Re2O7/ANN-550 exhibited the best performances. Based on the in situ Infrared spectroscopy, the in situ Raman spectroscopy, and the in-situ IR spectroscopy of chemisorbed ammonia and thermodesorption results, the use of ANN as Al2O3 precursors provided higher acidic OH group and higher Lewis acid sites, which were necessary for the formation of the 2nd rhenium oxide active species especially for low Re loading. The higher Bronsted acidity on the Re2O7/Al-com, on the other hand, produced higher amount of coke and C5+ products. In addition, the acid strength of the Lewis acid sites appeared to be another important factor determining metathesis activity of the supported Re2O7 catalysts.

Crystal structure of poly[di-aqua-(μ-2-carb-oxy-acetato-κ(3) O,O':O'')(2-carb-oxy-acetato-κO)di-μ-chlorido-dicobalt(II)

The asymmetric unit of the title polymer, [Co2(C3H3O4)2Cl2(H2O)2] n , comprises one Co(II) atom, one water mol-ecule, one singly deprotonated malonic acid mol-ecule (HMal(-); systematic name 2-carb-oxy-acetate) and one Cl(-) anion. The Co(II) atom is octa-hedrally coordinated by the O atom of a water mol-ecule, by one terminally bound carboxyl-ate O atom of an HMal(-) anion and by two O atoms of a chelating HMal(-) anion, as well as by two Cl(-) anions. The Cl(-) anions bridge two Co(II) atoms, forming a centrosymmetric Co2Cl2 core. Each malonate ligand is involved in the formation of six-membered chelate rings involving one Co(II) atom of the dinuclear unit and at the same time is coordinating to another Co(II) atom of a neighbouring dinuclear unit in a bridging mode. The combination of chelating and bridging coordination modes leads to the formation of a two-dimensional coordination polymer extending parallel to (001). Within a layer, O-Hwater⋯Cl and O-Hwater⋯O hydrogen bonds are present. Adjacent layers are linked through O-H⋯O=C hydrogen bonds involving the carb-oxy-lic acid OH and carbonyl groups.

Roles of individual radicals generated by a submerged dielectric barrier discharge plasma reactor during Escherichia coli O157:H7 inactivation

A submerged dielectric barrier discharge plasma reactor (underwater DBD) has been used on Escherichia coli O157:H7 (ATCC 35150). Plasma treatment was carried out using clean dry air gas to investigate the individual effects of the radicals produced by underwater DBD on an E. coli O157:H7 suspension (8.0 log CFU/ml). E. coli O157:H7 was reduced by 6.0 log CFU/ml for 2 min of underwater DBD plasma treatment. Optical Emission Spectra (OES) shows that OH and NO (α, β) radicals, generated by underwater DBD along with ozone gas. E. coli O157:H7 were reduced by 2.3 log CFU/ml for 10 min of underwater DBD plasma treatment with the terephthalic acid (TA) OH radical scavenger solution, which is significantly lower (3.7 log CFU/ml) than the result obtained without using the OH radical scavenger. A maximum of 1.5 ppm of ozone gas was produced during the discharge of underwater DBD, and the obtained reduction difference in E.coli O157:H7 in presence and in absence of ozone gas was 1.68 log CFU/ml. The remainder of the 0.62 log CFU/ml reduction might be due to the effect of the NO (α, β) radicals or due to the combined effect of all the radicals produced by underwater DBD. A small amount of hydrogen peroxide was also generated but does not play any role in E. coli O157:H7 inactivation.

Microwave Spectrum for a Second Higher Energy Conformer of Cyclopropanecarboxylic Acid and Determination of the Gas Phase Structure of the Ground State.

Microwave spectra for a higher-energy conformer of cyclopropanecarboxylic acid (CPCA) were measured using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer. The rotational constants (in megahertz) and centrifugal distortion constants (in kilohertz) for this higher-energy conformer are A = 7452.3132(57), B = 2789.8602(43), C = 2415.0725(40), DJ = 0.29(53), and DJK = 2.5(12). Differences between rotational constants for this excited-state conformation and the ground state are primarily due to the acidic OH bond moving from a position cis relative to the cyclopropyl group about the C1-C9 bond to the more stable trans conformation. Calculations indicate that the relative abundance of the higher-energy state should be 15% to 17% at room temperature, but the observed relative abundance for the supersonic expansion conditions is about 1%. The measurements of rotational transitions for the trans form of CPCA were extended to include all of the unique (13)C singly substituted positions. These measurements, along with previously measured transitions of the parent and -OD isotopologues, were used to determine a best-fit gas-phase structure.

Crystal structure of 4-(meth-oxy-carbon-yl)phenyl-boronic acid.

In the title compound, C8H9BO4, the meth-oxy-carbonyl group is rotated out of the plane of the benzene ring by 7.70 (6)°. In the crystal, mol-ecules are linked via pairs of O-H⋯O hydrogen bonds, involving the boronic acid OH groups, forming inversion dimers. The dimers are linked via O-H⋯O hydrogen bonds, involving a boronic acid OH group and the carbonyl O atom, forming undulating sheets parallel to (10-2). Within the sheets there are also C-H⋯O hydrogen bonds present, also involving the carbonyl O atom. The sheets are linked via C-H⋯π and offset face-to-face π-inter-actions between inversion-related mol-ecules [inter-centroid distance = 3.7843 (16) Å, inter-planar distance = 3.3427 (4) Å and offset = 1.744 Å], forming a three-dimensional structure.

Intrinsic Ladders of Affinity for Amino-Acid-Analogues on Boron Nitride Nanomaterials: A B3LYP-D2* Periodic Study

A systematic computational study of the gas-phase adsorption of different amino-acid-analogues (AA-an’s) on a (6,0) boron nitride nanotube (BNNT) and on a boron nitride monolayer (BNML) has been performed by means of B3LYP-D2* periodic calculations. The AA-an’s are CH3-R molecules, where R represents functional groups present in amino acid side chains, i.e., OH, COOH, CONH2, NH2, imidazole, guanidine, phenyl, phenol, indole, and CONHCH3. On (6,0) BNNT, AA-an species containing N electron donor groups (i.e., R = NH2, imidazole, and guanidine) are strongly chemisorbed through dative interactions between the N atom of the AA-an and a B atom of the nanotube and present the largest adsorption energies (ΔEads). For AA-an bearing aromatic rings (i.e., R = phenyl, phenol and indole) and R = CONHCH3, adsorption is driven by π-stacking interactions (with lower ΔEads values than the previous group), while for AA-an with O electron donor groups and H-bonding donor groups (i.e., R = OH, COOH, and CONH2) adsorption is ...

Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

In the present work, the generation and properties of Bronsted acidic bridging OH groups (Si(OH)Al) in Rh-, Ir-, Pd-, and Pt-containing zeolites Y were quantitatively investigated by multinuclear solid-state NMR spectroscopy. The number of Si(OH)Al groups formed per noble metal atom upon their reduction was found to be 0.3 to 1.3 instead of the theoretically expected values of 2 (Pd2+, Pt2+) or 3 (Rh3+, Ir3+). For zeolites Y with low noble metal loadings, a significantly lower acid strength of Si(OH)Al groups in comparison with those of H,Na–Y zeolites occurred. Interestingly, noble metal-containing zeolites Y with lower acid strength have a significant content of not completely reduced noble metal atoms with partially cationic character. The spatial distribution of Si(OH)Al groups in noble metal-containing zeolites Y was found to differ significantly from that in H,Na–Y zeolites. This effect is explained by the migration of a significant content of noble metal atoms into the sodalite cages of zeolites Y ...

Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5.

The reaction mechanism of the decomposition of ethoxy species to ethene and acidic OH groups on H-ZSM-5 was studied by IR spectroscopy using isotope-labeled ethanol. The concerted mechanism occurring on both the ethoxy (acid) site and the counterpart lattice oxygen was suggested by GC-MS analysis of evolved d2-ethene and IR observation of the recovery of OH s groups on acid sites from the decomposition of CH3CD2O- ethoxy species. The concerted mechanism was further confirmed by the estimation of activation energy for decomposition of CH3CH2O-, CH3CD2O-, and CD3CD2O- ethoxy species, 122 ± 3, 125 ± 3, and 140 ± 5 kJ mol(-1), respectively, where the kinetic isotope effect was observed for the cleavage of the CH or CD bond of the methyl group of the ethoxy species.

Simple synthesis of Al2O3 sphere composite from hybrid process with improved thermal stability for catalytic applications

Aluminium oxide spheres were synthesized by the hybrid process applying the biopolymer chitosan. After the calcination process the porous spheres were characterized by Chemical elemental analysis (XRF), X-ray diffraction (XRD), Scanning electron microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS), N2 adsorption–desorption isotherms, infrared spectroscopy (IR), and CO2 temperature programmed desorption (CO2-TPD). The effect of thermal treatment on surface properties of the oxide spheres was also evaluated by the catalytic ethanol dehydration reaction. The hybrid method produced interesting results related to the thermal stability against sintering process and consequently low decreases of surface area. The hybrid spheres calcination at 900 and 1200 °C produced a metastable phases of alumina with a high surface area, and nanometric crystallites. Additionally, the spheres of mixed silica-alumina synthesized by this method reveal the formation of porous spheres with highly acidic OH groups, which was suggested by the catalytic performance.

The Dynamic Nature of Brønsted Acid Sites in Cu–Zeolites During NOx Selective Catalytic Reduction: Quantification by Gas-Phase Ammonia Titration

Bronsted acid sites on Cu-exchanged zeolites can be titrated selectively using gaseous ammonia when NH3 saturation steps are followed by protocols that remove Lewis acid-bound and physisorbed NH3, such as purging in flowing wet helium at 433 K. NH3 titrates all H+ sites on small-pore chabazite zeolites (SSZ-13) and leads to the complete disappearance of infrared stretches for Bronsted acidic OH groups after saturation (433 K), in contrast with larger n-propylamine titrants that access only a small fraction (<0.25) of H+ sites on SSZ-13 under conditions sufficient to titrate all H+ sites on medium-pore ZSM-5 zeolites (323 K, 2 h). NH3 titration of the residual H+ sites present in Cu-exchanged SSZ-13 samples (Si/Al = 4.5, Cu/Al = 0–0.20) after oxidative treatments detects two fewer H+ sites per exchanged Cu2+ ion, as expected to maintain framework charge neutrality. NH3 titrants detect only one fewer H+ site (per Cu) after Cu-SSZ-13 samples undergo a reductive treatment in flowing NO and NH3 (473 K), however, indicating that each Cu2+ cation reduces to form a Cu+ and H+ site pair. In the context of low temperature (473 K) selective catalytic reduction (SCR) on high aluminum Cu-SSZ-13, we discuss the different mechanistic roles of residual H+ sites that remain after Cu2+ exchange, whose primary function appears to be NH3 storage, and of proximal H+ sites that are generated in situ upon Cu2+ reduction, whose role is to stabilize reactive NH4 + intermediates involved in the standard SCR oxidation half-cycle. We highlight how gaseous NH3 titrants can selectively count H+ sites on small-pore, Cu-exchanged zeolites and, in doing so, enable probing the dynamic nature of active sites and catalytic surfaces during SCR redox cycles.

Brønsted sites and structural stabilization effect of acidic low-silica zeolite A prepared by partial ammonium exchange

It is demonstrated for low-silica zeolite 25NH4,Na-A (nSi/nAl = 1.0) with an ammonium exchange degree of 25% that the formation of acidic bridging OH groups (Si(OH)Al) after thermal deammoniation is accompanied by a weak dealumination of the framework. As the extra-framework aluminum species mainly exist predominantly in the form of Al3+ cations, they partially neutralize negative framework charges. The remaining framework charges are compensated by Na+ cations and hydroxyl protons of Si(OH)Al groups. Therefore, a lower number of Si(OH)Al groups is formed than expected by the stoichiometry of the ammonium exchange. For zeolite 25NH4,Na-A, only 17% of the introduced ammonium ions form Si(OH)Al groups after thermal deammoniation. A benefit of the cationic extra-framework aluminum species (Al3+) is their stabilizing effect exerted on the remaining framework aluminum atoms and the whole structure of the obtained zeolite 25H,Na-A. 1H MAS NMR signals of acidic OH groups were observed at 3.6 and 4.8 ppm and assigned to Si(OH)Al groups in the α- and β-cages, respectively. A low-field signal at 13.3 ppm is probably due to Si(OH)Al groups, however, involved in H-bondings (Si(OH⋯O)Al) with hydroxyl protons directed to very near oxygen atoms, such as expected in double 4-rings of the LTA structure.

Characterization and Dynamics of the Different Protonic Species in Hydrated 12-Tungstophosphoric Acid Studied by2H NMR

Solid heteropolyacids (HPAs) are promising nonpolluting superacids used as catalysts and solid proton conductors. The catalytic and conducting properties of HPAs are very sensitive to the amount of hydration water present in the system, as water molecules tend to interact with the HPA acid protons to form [H3O]+ and [H5O2]+ ions. These ions constitute active species that govern the catalytic reaction pathways and the proton migration mechanism. Establishing the structure and mobility of protonic species could yield important information concerning the functions of material based on HPA hydrates. In this work, we have performed the analysis of both 2H NMR line shape and the evolution of T1, T2 relaxation with temperature for the deuterated analogue of the solid 12-tungstophosphoric acid (TPA × nH2O) at different hydration levels (0 < n < 6) in the wide temperature range of 103–503 K. This allowed us to characterize in detail the mobility of different protonic species, including acidic OH groups, water molecules, and hydroxonium ions. Kinetic parameters of internal and diffusional motions for different protonic species at different hydration levels n of TPA × nH2O were derived.

Intramolecular H/D Exchange of Ethanol Catalyzed by Acidic OH Groups on H-ZSM-5 Zeolite

IR observation of ethanol adsorption clarified the presence of the apparent intramolecular isotope exchange from CD3CH2OH to CHD2CH2OD on acidic OH groups of H-ZSM-5 zeolite. This reaction did not proceed with CD3OH nor CH3CD2OH, implying that the β-hydrogen of alcohol had interaction with the lattice oxygen adjacent to Al and that the reaction was mediated by isotope exchange of CD3 groups of ethanol and OH groups on zeolite.

Near-infrared laser-induced generation of three rare conformers of glycolic acid.

Structural transformations were induced in conformers of glycolic acid by selective excitation with monochromatic tunable near-infrared laser light. For the compound isolated in Ar matrixes, near-IR excitation led to generation of two higher-energy conformers (GAC; AAT) differing from the most stable SSC form by 180° rotation around the C-C bond. A detailed investigation of this transformation revealed that one conformer (GAC) is produced directly from the near-IR-excited most stable conformer. The other higher-energy conformer (AAT) was effectively generated only upon excitation of the primary photoproduct (GAC) with another near-IR photon. Once these higher-energy conformers of glycolic acid were generated in an Ar matrix, they could be subsequently transformed into one another upon selective near-IR excitations. Interestingly, no repopulation of the initial most stable SSC conformer occurred upon near-IR excitation of the higher-energy forms of the compound isolated in solid Ar. A dramatically different picture of near-IR-induced conformational transformations was observed for glycolic acid isolated in N2 matrixes. In this case, upon near-IR excitation, the most stable SSC form converted solely into a new conformer (SST), where the acid OH group is rotated by 180°. This conformational transformation was found to be photoreversible. Moreover, SST conformer, photoproduced in the N2 matrix, spontaneously converted to the most stable SSC form of glycolic acid, when the matrix was kept at cryogenic temperature and in the dark.

Differentiating Sulfopeptide and Phosphopeptide Ions via Resonant Infrared Photodissociation

The post-translational modifications sulfation and phosphorylation pose special challenges to mass spectral analysis due to their isobaric nature and their lability in the gas phase, as both types of peptides dissociate through similar channels upon collisional activation. Here, we present resonant infrared photodissociation based on diagnostic sulfate and phosphate OH stretches, as a means to differentiate sulfated from phosphorylated peptides within the framework of a mass spectrometry platform. The approach is demonstrated for a number of tyrosine-containing peptides, ranging from dipeptides (YG, pYG, and sYG) over tripeptides (GYR, GpYR, and GsYR), to more biologically relevant enkephalin peptides (YGGFL, pYGGFL, and sYGGFL). In all cases, the diagnostic ranges for sulfate OH stretches are established as 3580-3600 cm(-1) and can thus be distinguished from other characteristic hydrogen stretches, such as carboxylic acid OH, alcohol OH, and phosphate OH stretches.

Periodic, vdW-corrected density functional theory investigation of the effect of Al siting in H-ZSM-5 on chemisorption properties and site-specific acidity

Twelve crystallographically distinct Al substitution sites of H-ZSM-5 are modeled by periodic density functional theory using the vdW-DF functional. While the stability of Al substitution and Brønsted acid OH bond length at different active site positions are similar, the OH stretch frequency, SiOAl bond angle, and adsorption energies of various probe molecules differ notably without observable correlations between these properties. Comparison of adsorption energy values with and without van der Waals corrections demonstrates the significance of the inclusion of dispersion interactions. Our data indicate that theoretical investigations of H-ZSM-5 require a careful selection of the location of the active site.

Impact of Conventional and Microwave Heating on SAPO‐5 Formation and Brønsted Acidic Properties

AbstractThe hydrothermal crystallization of SAPO‐5 molecular sieves with Si mole ratios in the range of 0.05 to 0.13 was performed by either conventional or microwave heating to compare the influence of these two techniques on the isomorphous substitution of phosphorus by silicon atoms in the aluminophosphate framework. An extensive characterization of the obtained silicoaluminophosphates by ICP‐OES, SEM, XRD, TPDA, and MAS NMR spectroscopy indicated that conventional heating (drying oven) led to a better crystallinity and a higher content of isolated framework silicon atoms than microwave heating. While microwave heating has the advantage of reducing the crystallization time and conventionally prepared SAPO‐5 materials show better incorporation of isolated silicon atoms into the AFI framework according to the substitution mechanism SM IIa. This lower SM IIa substitution of tetrahedral framework sites by isolated silicon atoms in microwave‐prepared SAPO‐5 materials is the reason for their lower density of Brønsted acidic bridging OH groups [Si(OH)Al]. In contrast, the density of defect OH groups, such as weakly acidic SiOH groups, is higher than for conventionally prepared samples.

Experimental Raman and IR spectral and theoretical studies of vibrational spectrum and molecular structure of Pantothenic acid (vitamin B5)

Vibrational spectrum of Pantothenic acid has been investigated using experimental IR and Raman spectroscopies and density functional theory methods available with the Gaussian 09 software. Vibrational assignments of the observed IR and Raman bands have been proposed in light of the results obtained from computations. In order to assign the observed IR and Raman frequencies the potential energy distributions (PEDs) have also been computed using GAR2PED software. Optimized geometrical parameters suggest that the overall symmetry of the molecule is C1. The molecule is found to possess eight conformations. Conformational analysis was carried out to obtain the most stable configuration of the molecule. In the present paper the vibrational features of the lowest energy conformer C-I have been studied. The two methyl groups have slightly distorted symmetries from C3V. The acidic OH bond is found to be the smallest one. To investigate molecular stability and bond strength we have used natural bond orbital analysis (NBO). Charge transfer occurs in the molecule have been shown by the calculated highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies. The mapping of electron density iso-surface with electrostatic potential (ESP), has been carried out to get the information about the size, shape, charge density distribution and site of chemical reactivity of the molecule.

Determination of organic matter and organic matter to organic carbon ratios by infrared spectroscopy with application to selected sites in the IMPROVE network

Mass of ambient particulate organic matter (OM) is often estimated by multiplying the organic carbon (OC) mass by a fixed factor that typically ranges from 1.4 to 1.8. In this paper, we develop a non-destructive, mid-infrared spectroscopic (MIR) technique to measure OM in PM2.5 collected on PTFE filters (commonly called “teflon” filters). MIR techniques measure absorption by functional groups within organic molecules; that is, carbon atoms bonded to oxygen (O) or hydrogen (H), O bonded to H and other elements bonded together in organic molecules that comprise OM. We developed laboratory standards of atmospherically relevant organic compounds as the basis for calibrating the MIR absorption to the moles of functional groups. A multivariate regression technique was used to develop calibrations for quantifying alkane CH, alcohol OH, carboxylic acid OH, and carbonyl, which likely comprise the bulk of OM in most ambient samples. OM is estimated as the sum of masses attributed to these functional groups. The precision of the OM measurement is 6.9 μg (relative precision is 7%) and the minimum detection limit is 4.8 μg, corresponding to an ambient concentrations of 0.21 μg m−3 and 0.15 μg m−3 respectively, for the sampling protocol used here.The method was employed to estimate OM, OC (estimated as the sum of the mass of carbon in the alkane CH and carbonyl functional groups) and OM/OC from one year of routinely collected filters at seven Interagency Monitoring of Protected Visual Environments (IMPROVE) sites. In the IMPROVE network, OC is measured using a thermal optical method and OM is estimated for regional haze tracking simply as 1.8 × OC. Using the MIR technique on one year of samples from 7 IMPROVE sites, the median OM/OC ratio was 1.69 with the 10th and 90th percentiles of 1.46 and 2.01. Phoenix, AZ had the lowest annual-median value of 1.56 and Mesa Verde, CO had the highest of 1.83. For more than half of the sites, the lowest monthly-median OM/OC ratio occurred in winter. The sample, site median and seasonal median OM/OC ratios obtained from MIR analysis indicate that a single estimate of OM/OC does not represent the observed variability in OM/OC.