Selective Hydrodeoxygenation of Guaiacol Catalyzed by Platinum Supported on Magnesium Oxide

Supporting Information

Selective hydrodeoxygenation of guaiacol catalyzed by platinum supported on magnesium oxide

Tarit Nimmanwudipong,Ceren Aydin,Jing Lu, Ron C. Runnebaum, Kevin C. Brodwater,Nigel D. Browning, David E. Block, Bruce C. Gates*

Product analyses

Samples of the liquid flowing from the separator were analyzed with a gas chromatograph (Agilent 7890A) equipped with a mass selective detector (MSD, Agilent 5975C). The GC parameters were as follows: sample size, 1 μL; injection temperature, 543 K; split ratio, 1:20. The temperature program started at 343 K; the temperature ramp was 30 K/min to 388 K, following by a 5-K ramp to 403 K, a 30-K ramp to 453 K, a 1.25-K ramp to 473 K, a 15-K ramp to 503 K, and a 5-K ramp to 513 K (followed by a 6-min hold). The MSD was operated with a scanning rate of 3.66 scan/s with a range from 1−400 atomic mass units. A constant flow rate of helium carrier gas of 2.4 mL/s was used with a starting pressure of 260 kPa. Peaks were identified on the basis of the mass spectra by matching to a library of NIST spectra

A gas chromatograph equipped with an FID (Agilent 7890A) was used to determine the concentrations of products in the liquid samples. GC-FID parameters were similar to the GC-MS parameters. The FID temperature was set at 573 K; the H2 flow rate was 30 mL(NTP)/min, and the air flow rate was 400 mL(NTP)/min. The flow rate through the detector was held constant at 25 mL/min, with N2 as a make-up gas. A ten-point calibration (5−20,000 ppm) was performed by using the following compounds individually mixed with guaiacol: cyclohexane, benzene, toluene, anisole, cyclohexanone, o-cresol, catechol, 4-methylguaiacol, and 3-methylcatechol. Concentrations of other compounds were estimated by using semi-quantitative values based on data obtained with similar components having the same numbers of carbon atoms.

The gas effluent from the separator was analyzed with a GC-RGA (Agilent 7890A), equipped with three sample loops, five columns, and three detectors (one FID and two thermal conductivity detectors (TCDs)). Peak identification for fixed gases was made by comparison with a Praxair RGA gas calibration standard (see supplementary data, Table S1). The data were analyzed with Agilent MSD Chemstation software G170EA rev E.02.00.493.

Gas Chromatography Instrumentation

A GC (Agilent 7890A), equipped with three sample loops, five columns, and three detectors (one FID and two TC detectors), was used to analyze the gas effluent from the separator. Each of the sample loops was 500 L in volume. Hydrocarbons were separated in an HP-Al/S (19095P-S25, 50 m long/0.53 mm in I.D./15 m in film thickness) Agilent J&W capillary column by using a helium carrier gas flow rate of 27 mL/min, and the components were quantified by analysis with an FID. The FID was operated at 300 mL/min zero-air and 25 mL/min H2 flow rates. Fixed gases and methane were separated with three Agilent 1/8-in stainless-steel packed columns mounted in series: HayeSep Q (6 ft), HayeSep N (8 ft), and Molsieve 13X (10 ft), and the components were quantified with a TCD with helium carrier gas at a pressure of 70 kPa. H2 was separated in a 4-ft Molsieve 13X packed column and quantified with a TCD by using N2 carrier gas. Temperature and carrier gas flow ramps were used to improve the retention time and separation of compounds. Gas samples were taken online at approximately 30-min intervals; each of the sample loops was actuated, nearly simultaneously, to load the flow paths to each of the detectors and to characterize the gas stream. Peak identification was carried out by comparison with a NIST traceable Agilent Technologies/Praxair RGA gas calibration standard (5184-3545, Lot No. 091509R). Single-point calibrations, determined by using data collected with compounds (Table S1) in the gas calibration standard, were used to quantify products in the gas stream.

Composition of gas calibration standard.

Compound / Concentration (mol %)
H2 / 12.1
N2 / 64.3
CO / 1.00
CO2 / 2.99
Methane / 5.00
Ethane / 3.99
Ethylene / 2.01
Acetylene / .998
Propane / 2.01
Propylene / 0.998
1,2-Propadiene / 0.964
Methyl acetylene / 0.987
Isobutane / 0.300
n-Butane / 0.299
1-Butene / 0.299
Isobutylene / 0.294
trans-2-Butene / 0.300
cis-2-Butene / 0.299
1,2-Butadiene / 0.297
Isopentane / 0.100
n-Pentane / 0.100
1-Pentene / 0.0997
cis-2-Pentene / 0.0945
trans-2-Pentene / 0.0990
2-Methyl-2-butene / 0.0485
n-Hexane / 0.0499

X-ray Absorption Spectroscopy

X-ray absorption spectra were recorded at beam line X18-B at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The storage ring electron energy and ring currents were 2.8 GeV and 200–300 mA, respectively. A Si [111] double crystal monochromator was used, which was detuned to 80% of maximum intensity to reduce the interference of higher harmonics present in the X-ray beam. The mass of each sample (approximately 0.25 g) was chosen to give an absorbance in the range of 1.5 to 3.0 calculated at 50 eV above the Pt LIII edge (11564 eV). In an N2-filled glovebox at NSLS, the sample was pressed into a wafer and placed in a cell1 and maintained under vacuum (10-5 kPa) at liquid nitrogen temperature during the data collection. X-ray intensity data were collected in transmission mode by use of ion chambers mounted on each end of the sample cell. For calibration purposes, measurement of the absorption of a platinum foil was carried out simultaneously, with the foil placed in the beam path. Ion chambers for the incoming beam (placed before the sample), for the beam that had passed through the sample cell (placed after the sample), and for the beam transmitted by the reference foil (placed after the sample cell) had the following compositions and gas flow rates, respectively: 100% N2 (at a flow rate of 35 mL/min), 90% argon and 10% krypton, and 100% argon (at a flow rate of 15 mL/min).

Extended X-Ray Absorption Fine Structure (EXAFS) Data Analysis

Analysis of the EXAFS data was carried out with the software ATHENA of the IFEFFIT2.3 package and the software XDAP developed by Vaarkamp et al.4 Each spectrum that was analyzed was the average of four spectra. ATHENA was used for edge calibration, alignment, and averaging the scans. XDAP was used for deglitching, background removal, normalization, and conversion of the data into an EXAFS (χ) file. A “difference-file” technique was applied with XDAP for determination of optimized fit parameters. Each spectrum was processed by fitting a second-order polynomial to the pre-edge region and subtracting this from the entire spectrum. The functional that was minimized and the function used to model the data are given elsewhere.5 The background was subtracted by using cubic spline routines. Reference backscattering amplitudes and phase shifts were calculated with the software FEFF76 from crystallographic data characterizing each reference material. Crystallographic coordinates of the platinum metal7 was used for the Pt–Pt1st and Pt–Pt2nd contributions. Iterative fitting was done in R (distance) space with the unfiltered, Fourier-transformed χ data until optimum agreement was attained between the calculated k0-, k1-, k2-,and k3-weighted EXAFS data and the postulated model (k is the wave vector). The number of parameters used in the fitting was always less than the statistically justified number, computed with the Nyquist theorem:8n = (2ΔkΔr/π) + 1, where Δk and Δr, respectively, are the k and R (distance) ranges used in the fitting (Table S1).

Table S1. EXAFS parameters characterizing γ-Al2O3 and MgO supported platinum catalysts.

Support / Absorber – back-scatterer pair / N / R(Å) / 103×Δσ2 (Å2) / ΔE0 (eV) / k-range (Å-1) / R-range
(Å) / Error in
EXAFS function[b] / Good-ness of fit[c]
γ-Al2O3 / Pt–Pt1st / 8.5 / 2.74 / 8.3 / -1.18 / 4.12–13.80 / 1.0–4.0 / 0.001 / 15
Pt–Pt2nd / 2.3 / 3.85 / 9.4 / -0.19
MgO / Pt–Pt1st / 8.1 / 2.71 / 9.3 / -7.2 / 4.35–14.02 / 1.0–4.0 / 0.0008 / 11
Pt–Pt2nd / 2.5 / 3.86 / 9.9 / -4.5

[a] Notation: N, coordination number; R, distance between absorber and backscatterer atoms; Δσ2, disorder factor; ΔE0, Inner potential correction. Error bounds (accuracies) characterizing the structural parameters obtained by EXAFS spectroscopy are estimated to be as follows: N, ± 20%; R, ± 0.02Å; Δσ2, ± 20%; and ΔE0, ± 20%. [b] The error in the data was calculated as the root mean square of the value obtained from the subtraction of smoothed χ data from the background-subtracted experimental χ values. [c] Goodness of fit values were calculated with the software XDAP, as follows: the terms χmodel and χexp are the model and experimental EXAFS values, respectively; σexp is the error in the experimental results; ν is the number of independent data points in the fit range; and NPTS is the actual number of data points in the fit range; Nfree is the number of free parameters. [d] Number of statistically justified parameters was calculated by the Nyquist theorem as follows: number of justified parameters = n= (2ΔkΔR/π) + 2, where Δk and ΔR are the k- and R- ranges used the fitting.

Electron Microscope Imaging

Images of the samples were obtained with a JEOL JEM-2100F electron microscope at the University of California, Davis. The microscope is equipped with a field emission gun (FEG), operated at 200 kV, with a CEOS hexapole probe (STEM) aberration corrector. The images were captured by a high-angle annular dark-field (HAADF) detector with a collection semiangle of 75–200 mrad and a probe convergence semiangle of 17.1 mrad. Prior to imaging of the sample, the aberration corrector was aligned with a Pt/Ir on holey carbon standard sample (SPI supplies) until atomic resolution of the metals was achieved and lattice spacings of the metals in the standard sample were confirmed. Each TEM sample was prepared by using a lacey carbon, 300-mesh copper grid (Ted-Pella) that was dipped into the powder sample. After the excess powder had been shaken off of the grid, the TEM grid was loaded onto the microscope holder and the TEM holder was then inserted into the microscope.

Particle Size Measurement of HAADF-STEM Images.

For each particle, an intensity profile was obtained by using the Digital Micrograph software (Gatan). Line profiles were then transferred to OriginPro for baseline correction. Background subtracted profiles of the clusters were fitted to a Gaussian distribution function in OriginPro, and full-width-half-maximum (FWHM) values of the fitted peak were reported as the diameter of each platinum particle.

Table S2:Most abundant and tracea products formed in the conversionb of guaiacol catalyzed by Pt/γ-Al2O3 (liquid sample). Compounds were identified by using the NIST EI mass spectral database; some were confirmed by using authentic standards.

Product / Classification based on abundance in product streamc / Basis for identification of product / Basis for quantification of product
benzene / minor / standard sample / FID calibration curve
anisole / minor / standard sample / FID calibration curve
cyclohexanone / minor / standard sample / FID calibration curve
toluene / minor / standard sample / FID calibration curve
phenol / major / standard sample / FID calibration curve
2-methylphenol
(o-cresol) / minor / standard sample / FID calibration curve
1,2-benzenediol
(catechol) / major / standard sample / FID calibration curve
1,2-benzenediol-3-methyl
(3-methylcatechol) / major / standard sample / FID calibration curve
2-methoxy-3-methylphenol
(3-methylguaiacol) / minor / MS EI database / FID calibration curve
(Use 4-methylguaiacol)
2-methoxy-6-methylphenol
(6-methylguaiacol) / minor / MS EI database / FID calibration curve
(Use 4-methylguaiacol)
1,2-dimethoxybenzene
(veratrole) / minor / standard sample / FID calibration curve
cyclohexene / trace / standard sample / n/a
cyclohexane / trace / standard sample / n/a
1-methoxycyclohexane / trace / MS EI database / n/a
p-xylene / trace / MS EI database / n/a
cyclohexanol / trace / standard sample / n/a
2-methylcyclohexanone / trace / MS EI database / n/a
3-methylcyclohexanone / trace / MS EI database / n/a
2-methylanisole / trace / standard sample / n/a
4-methylanisole / trace / standard sample / n/a
2-methoxy-4-methylphenol
(4-methylguaiacol) / trace / standard sample / n/a
2-methoxy-5-methylphenol
(5-methylguaiacol) / trace / MS EI database / n/a
2,3-dimethylphenol / trace / MS EI database / n/a
2,5-dimethylphenol / trace / MS EI database / n/a
2,6-dimethylphenol / trace / standard sample / n/a
3,4-dimethylphenol / trace / MS EI database / n/a
2,3,5-trimethylphenol / trace / MS EI database / n/a
2,3,6-trimethylphenol / trace / MS EI database / n/a
2,4,6-trimethylphenol / trace / MS EI database / n/a
3,4,5-trimethylphenol / trace / MS EI database / n/a
water / trace / MS EI database / n/a
methanold / minor / MS EI database / n/a

aIdentifications of some trace products were not confirmed with standard samples; therefore, for example, substituted benzenes and substituted phenols other than those listed are possible products.

bConversion conditions: temperature, 573 K; WHSV, 19.8 ± 0.1 (g of guaiacol)/(g of catalyst × h); initial conversion of guaiacol, approximately 0.075.

cA product was classified as “major” when its response in a chromatogram was greater than 1.2 × 107 pico-Amps (pA); as “minor” when its response was between 1.0 × 106 and 1.2 × 107 pA; and as “trace” when its response was less than 1.0 × 106 pA.

dMethanol was observed in liquid samples; however, its concentration in the gas phase was not quantified.

Table S3: Most abundant and tracea products formed in the conversionb of guaiacol catalyzed by Pt/MgO (liquid sample). Compounds were identified by using the NIST EI mass spectral database; some were confirmed by using authentic standards.

Product / Classification based on abundance in product streamc / Basis for identification of product / Basis for quantification of product
Benzene / minor / standard sample / FID calibration curve
Anisole / minor / standard sample / FID calibration curve
Cyclopentanone / major / standard sample / FID calibration curve
Cyclohexanone / minor / standard sample / FID calibration curve
Phenol / major / standard sample / FID calibration curve
2-methylphenol
(o-cresol) / minor / standard sample / FID calibration curve
1,2-benzenediol
(catechol) / major / standard sample / FID calibration curve
1,2-dimethoxybenzene
(veratrole) / minor / standard sample / FID calibration curve
2-pentanone / trace / MS EI database / n/a
2-pentanol / trace / MS EI database / n/a
2-cyclopenten-1-one / trace / MS EI database / n/a
Cyclopentanol / trace / MS EI database / n/a
2-hexanone / trace / MS EI database / n/a
3-hexanone / trace / MS EI database / n/a
Cyclohexanol / trace / standard sample / n/a
2-methylcyclopentanone / trace / MS EI database / n/a
2-methylcyclohexanone / trace / MS EI database / n/a
2-methoxycyclohexanone / trace / standard sample / n/a
Water / trace / MS EI database / n/a
methanold / minor / standard sample / n/a

aIdentifications of some trace products were not confirmed with standard samples; therefore, for example, substituted benzenes and substituted phenols other than those listed are possible products.

bConversion conditions: temperature, 573 K; WHSV, 11.0 (g of guaiacol)/(g of catalyst × h); initial conversion of guaiacol, approximately 0.075.

dMethanol was observed in liquid samples; however, its concentration in the gas phase was not quantified.

Table S4. Products of conversion of guaiacol catalyzed by Pt/γ-Al2O3 and Pt/MgO (liquid product streams).a

Product / Selectivity to product in reaction catalyzed by Pt/MgO in the presence of H2b / Selectivity to product in reaction catalyzed by Pt/γ-Al2O3 in the presence of H2c
Benzene / 0.0002 / 0.004
Anisole / 0.002 / 0.011
cyclopentanone / 0.20 / 0.010
cyclohexanone / 0.050 / 0.031
Phenol / 0.60 / 0.44
o-cresol / 0.004 / 0.009
1,2-dimethoxybenzene / 0.007 / 0.024
3-methylguaiacol / - / 0.009
6-methylguaiacol / - / 0.032
Catechol / 0.11 / 0.29
3-methylcatechol / - / 0.10

a Data were extrapolated to zero time on stream, and thus represent approximate initial selectivities determined at weight hourly space velocity of 1.0 (g of reactant)/(g of catalyst · h), a pressure of 140 kPa, and a temperature of 573 K. Selectivity is defined as yield [mol product formed/mol of organic reactant fed]/conversion [mol of organic reactant consumed/mol of organic reactant fed].

b100 mL/min gas feed rate, 30% H2/70% helium; feed molar ratio of H2 to the organic reactant was 15. Approximate initial conversion was 0.18

c100 mL/min gas feed rate, 30% H2/70% helium; feed molar ratio of H2 to the organic reactant was 15. Approximate initial conversion is 0.20

Figure S1: HAADF-STEM images and particle size distributions of platinum supported on MgO (left) and on γ-Al2O3 (right) after use as catalysts for guaiacol conversion.

Fig. S2Selectivity for the formation of benzene (squares) and cyclohexanone (triangles)in the conversion of guaiacol catalyzed by Pt/MgO; reaction conditions are stated in the text. Data for each product were fitted with a straight line and extrapolated to zero conversion; intercepts of regression lines significantly different from zero selectivity at zero conversion (analyzed with 95% confidence limits) indicate primary products, in this case cyclohexanone, and that not significantly different from zero (analyzed with 95% confidence limits) are considered to be evidence of non-primary products, in this case benzene. However, cyclohexanone cannot be formed directly from guaiacol, thus it should be a non-primary product.

Fig. S3Selectivity for the formation of anisole(closed squares) and o-cresol (open squares)in the conversion of guaiacol catalyzed by Pt/MgO; reaction conditions are stated in the text. Data for each product were fitted with a straight line and extrapolated to zero conversion; intercepts of regression lines significantly different from zero selectivity at zero conversion (analyzed with 95% confidence limits) indicate primary products, in this case both anisole and o-cresol. However, o-cresol cannot be formed directly from guaiacol, thus it should be a non-primary product.

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