Decarboxylation of Diunsaturated Linoleic Acid to Heptadecane over

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Kinetics, Catalysis, and Reaction Engineering

Decarboxylation of Diunsaturated Linoleic Acid to Heptadecane over Zeolite Supported Pt/ZIF-67 Catalysts James Crawford, and Moises A Carreon Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02799 • Publication Date (Web): 02 Sep 2018 Downloaded from http://pubs.acs.org on September 2, 2018

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Industrial & Engineering Chemistry Research

Decarboxylation of diunsaturated Linoleic Acid to Heptadecane over Zeolite Supported Pt/ZIF-67 Catalysts James M. Crawford and Moises A. Carreon* Department of Chemical and Biological Engineering, Colorado School of Mines, United States, Golden, CO 80401, USA *Corresponding author: [email protected]

Abstract Diunsaturated linoleic acid was deoxygenated in H2, CO2, and N2 atmospheres over 0.3wt% Pt/ZIF-67/Zeolite 5A bead catalysts. Nearly complete conversion was observed in H2 and N2 atmospheres (≥95%).

When N2 and CO2 were employed during the reaction, the primary

reaction pathway was decarboxylation. In the case of H2, the formation of octadecane in the liquid product suggests that hydrodeoxygenation is a competing pathway to decarboxylation. Yields to heptadecane under H2, CO2, and N2 were 65.3, 63.5%, 58.4%, respectively. The best catalyst recyclability was observed in CO2 atmospheres where activity decreased only ~1% on regeneration. Activity losses were higher in nitrogen and hydrogen, 3.8 and 10.7%, respectively. An investigation of esters in the reactants and products led to an alternative method for the evaluation of total conversion (% deoxygenation). Strong correlations between titrimetric assays and ATR-FTIR were observed. Keywords: lipid biomass; unsaturated fatty acid; decarboxylation; linoleic acid; heptadecane

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1. Introduction Renewable fuels hold great potential in leveraging untapped resources and reducing carbon emissions. Production of these fuels requires a low cost, non-edible, and abundant feedstock. Lipid biomass is a highly suitable candidate, derived from vegetable oil, micro-algae oil, and animal fats. The composition of these oils varies widely depending on the feedstock, giving a combination of saturated, monounsaturated, and polyunsaturated fatty acids.1 Most studies have focused on the conversion of saturated and monounsaturated fatty acids including lauric (12:0), palmitic (16:0), stearic (18:0), and oleic acid (18:1) over noble metal catalysts, showing success in the formation of liquid fuel hydrocarbon products.2–4 Typical deoxygenation pathways for fatty acids include hydrodeoxygenation and decarboxylation under hydrogen or inert gas, respectively. Hydrodeoxygenation is the most developed process but requires a large supply of hydrogen which incurs large costs, safety concerns, and negative environmental impacts.5,6 Decarboxylation is an effective alternative which results in the removal of the carboxylate group as carbon dioxide, leaving linear hydrocarbons such as heptadecane (C17). Fatty acid deoxygenation has been widely studied over diverse solid catalysts, including Pt/C,7 SiO2,8 CeO2,9 zeolites and hydrotalcite,10 SAPO-11 and chloride Al2O3,11 Pd/C,12 activated carbon,13 metal nitrates, metal nitrides, supported on γ-Al2O3,14 hydrotalcite,15 Sn hydroxide,16 Fe,17 Ni/MgO-Al2O3,18 H3PO4/Al2O3,19 aluminosilicate, titanium, magnesium, zirconium and cerium oxide.20 Previously, our group reported a catalytic system consisting of zeolite 5A beads, cobalt-based zeolitic imidazolate framework-67 (ZIF-67) layers, and Pt.2,4,21 Zeolite 5A beads were employed as catalytic supports due to their enhanced chemical and thermal stability. Furthermore, as compared to powders, beads are easier to recycle and can be fully recovered, and therefore are

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amenable to potential scale-up.22 The ZIF-67 layer grown on the 5A bead promoted platinum dispersion and decreased platinum leaching, which gave a more active and stable catalyst.2,4 Platinum is the catalytically active metal that converts fatty acids into liquid hydrocarbons. In addition, Co has been suggested as co-catalysts or promoter for hydrodeoxygenation reactions.4,23–26 To further understand the capabilities of the Pt/ZIF-67/Zeolite 5A bead catalytic system, it is important to study the conversion of common polyunsaturated fatty acids such as linoleic acid. Linoleic acid is found at high concentrations in non-edible Karanja, Jatropha, and micro-algae oil, making it an important model compound.27–29 Linoleic acid deoxygenation has been studied over several catalysts including platinum, palladium, and ruthenium supported on carbon or alumina at loadings greater than 5wt%30–32, at loadings between 1-3wt%22,33,34, under severe and mild hydrothermal conditions,22,32 over platinum supported on mesoporous carbon34, and over platinum-tin systems supported on carbon.35 No studies in the literature have shown selectivity for heptadecane higher than 1% at platinum loadings below 1wt%. Additionally, supports aside from carbon remain largely unexplored for the conversion of polyunsaturated fatty acids. Herein, we report the deoxygenation of linoleic acid over 0.3wt% Pt/ZIF-67/Zeolite 5A bead catalysts. The effect of the gas atmosphere on the reaction pathway was studied for nitrogen, carbon dioxide, and hydrogen. Additionally, complex fatty acids and ester isomers, which were challenging to identify by gas chromatography, were investigated by comparing titrimetric acid and ester values with attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) resulting in strong correlations and modifications to the overall deoxygenation conversion calculations.



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2. Experimental Section 2.1 Preparation and Characterization of Catalysts Pt/ZIF-67 layered zeolite 5A bead catalysts were synthesized as follows. Two solutions were prepared: 0.45 g cobalt nitrate hexahydrate (Sigma-Aldrich, ACS reagent ≥98%) in 3 mL deionized water and 5.5 g 2-methylimidazole (Sigma-Aldrich, 99%) in 20 mL deionized water. The solutions were combined and stirred at room temperature for 6 hours. The resultant solution was added to a 100 mL PTFE-lined autoclave with 5 g of zeolite 5A beads. The autoclave was sealed and heated to 150°C for 6 hours with a heating and cooling rate of 10°C/min. After the hydrothermal treatment, the ZIF-67 covered 5A beads were rinsed with deionized water and dried overnight at 100°C. A second layer was applied by the same method. Next, 0.057 g of Pt(NH3)4NO3 (Sigma-Aldrich, 99.995% trace metal basis) was dissolved in deionized water. The ZIF-67 covered 5A beads, with a final weight of 5.715 g, were added to this Pt solution, stirred thoroughly, and dried overnight at 100°C. Fresh and spent catalysts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller surface area (BET), inductively coupled-atomic emission spectroscopy (ICP-AES), and thermogravimetric analysis (TGA). For XRD (Siemens, Kristalloflex800, 25 mA, 30 kV, CuKα radiation) beads were crushed into a fine powder. FE-SEM images were obtained using a field emission gun and accelerating voltage of 5 kV (JEOL ISM-7000F). BET surface area was obtained from nitrogen isotherm data collected at 77 K (Micromeritics, ASAP 2020). All samples were degassed at 300°C for 8 hours. For ICP-AES, fresh and spent samples were first dried in vacuo at 100°C and weighed precisely (Metteler Toledo, AX26 DeltaRange). Samples were then digested in 2 mL of 10 M nitric acid and 1.5 mL of aqua regia for 24 hours prior to analysis (Perkin-Elmer, ICP-


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AES) by EPA method 200.7. TGA profiles (TA Instruments, Q500) were measured under nitrogen flow at 50 mL/min and a 10°C/min ramp rate. 2.2 Reaction Procedures Prior to the reaction, all catalysts were heated to 150°C for 2 hours to remove any physisorbed water. The catalyst was loaded with linoleic acid (Sigma-Aldrich, Technical grade, 69% by GCMS analysis) in a 100 mL stainless steel stirred-batch reactor (Parr, 4560) at a 1:1 mass ratio (1:333 mass ratio of platinum to linoleic acid). The reactor was flushed with the desired gas under constant flow for 5 minutes to remove stagnant air. The reactor was then sealed and pressurized to 20 bar followed by rapid heating to 320°C at a stir rate of 200 rpm. Additional experiments without stirring and at 400 rpm were carried out for selected samples to rule out mass transfer limitations. At the explored stirring rates

mass transfer limitations can be

neglected (Table S1). On reaching 320°C, the reaction was run for 2 hours. After the reaction, the reactor was quenched to room temperature using an ice bath. Liquid products were pipetted from the reactor and stored in 10 mL falcon tubes for centrifugation and further analysis. The spent catalysts were rinsed 3 times with hexane then methanol, followed by regeneration in air at 300°C for 12 hours (10°C/min heating and cooling rate). After regeneration the catalyst was either collected for characterization or exposed to an additional reaction. 2.3 Liquid Product Analysis The obtained liquid product from the reaction was centrifuged at 4000 rmp for 5 minutes. The supernatant was collected for gas chromatography and titrimetric analysis. Liquid hydrocarbon distribution was obtained by gas chromatography (Agilent GC, 6980N) equipped with a HP-5 molecular sieve column (30 m x 250 µm x 0.25 µm) and mass spectrometer detector (Agilent MSD, 5973N). Prior to GC-MS analysis, products were exposed to a silylation step to volatilize



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remaining acids in the products.3,10,21,31,36 Specifically, 50 µL of products were combined in a 2 mL glass vial with 100 µL N,O-bis(trimethyl)trifloroacetamide, BTSFA (Sigma-Aldrich, ≥99.0%) and 1,850 µL of hexane. This solution was capped and heated to 60°C for 1 hour (10°C/min). After silylation, 0.2 µL of solution was injected (Agilent AS, 7683B) on the column with a split ratio of 100:1 with He as the carrier gas. The oven program was 100°C for 5 min, 1°C/min ramp to 300°C, hold 300°C for 2 min. An external standard was evaluated for C8-C20 alkanes (Sigma-Aldrich, analytical standard) for complete quantification of the GC-MS results. Branched and n-alkanes were assumed to have the same response factor from the calibration (Table S2). The catalytic conversion of the fatty acid was calculated by the removal of the carboxylic acid groups and ester groups as a combined percent deoxygenated. Specifically, this value was calculated by the acid value (AV) test (ASTM D974) and the ester value (EV) using Equation 1: EV = SV – AV

(1)

where the saponification value (SV) was determined by ASTM D5558. Therefore, the conversion, XTOT, of fatty acids and esters was calculated by Equation 2:

=

+ − + ∗ 100 +

( 2)

The selectivity to heptadecane, SC17, was calculated from the percentage of heptadecane with respect to the other liquid products in the hydrocarbon distribution from the GC-MS. The yield, YC17, was calculated by multiplying the selectivity by the conversion. ATR-FTIR (Thermo Scientific, Nicolet 4700) was conducted on a ZnSe crystal, 64 scans, 700-4000 cm-1, 4 cm-1 resolution, 40 aperture, 1.899 rate, MCT/A, KBr beam splitter. ATR-FTIR peak areas were calculated by Spectragryph 1.2.8 optical microscopy software and were normalized to the largest peak before analysis. Correlations for ATR-FTIR peaks and titrimetric acid and ester values were 5 ACS Paragon Plus Environment

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constructed using stearic acid (Sigma-Aldrich, 99%), oleic acid (Alfa, 90%), and technical grade linoleic acid (Table S3). 3. Results and Discussion 3.1 Effect of Reaction Gas on Heptadecane Selectivity Catalytic results from the deoxygenation of linoleic acid under different gas atmospheres over 0.3wt% Pt/ZIF-67/zeolite 5A catalysts are shown in Table 1. Hydrogen atmospheres resulted in the highest yield to heptadecane, 65.3%, while also resulting in the largest loss of activity when recycled, ~11%. Hydrodeoxygenation was a competing reaction mechanism under hydrogen atmospheres, as indicated by the formation of octadecane (C18). This behavior was observed in our previous reports for the deoxygenation of palmitic acid and lauric acid.21 The presence of hydrogen during the reaction led to a relatively low concentration of short hydrocarbons (C7-11). Under hydrogen atmospheres, no unsaturated products were observed, likely due to the reducing abilities of the gas. This was corroborated by the ATR-FTIR spectra of the products, as no =CH stretch was observed at 3004 cm-1 (Figure 1). Additionally, the products reached nearly complete decarboxylation and deesterification evidenced by the disappearance of the –COOH group at 1707 and the C=O stretch at 1740 cm-1.

Table 1.

Product distribution for the deoxygenation of linoleic acid over 0.3wt% Pt/ZIF-

67/Zeolite 5A beads. Reaction conditions: t = 2 h, T = 320°C, P = 20 bar. XTOT=conversion; SC17=selectivity to heptadecane; YC17= yield to heptadecane

Catalyst Fresh Pt ZIF-67/Zeolite 5A Recycled Pt ZIF-67/Zeolite 5A Fresh Pt ZIF-67/Zeolite 5A

Gas CO2 H2

XTOT (%)

Hydrocarbon distribution (%) C7

C8

C9

C10

C11

C15

C17

C18

Other

SC17

YC17

88.2

6.5

4.7

2.5

2.0

2.0

5.6

72.0

0.0

4.6

72.0

63.5

78.3

3.3

2.2

1.5

1.3

1.2

5.7

80.6

0.0

4.2

80.6

63.1

97.4

0.9

0.8

0.8

0.8

0.8

3.2

67.0

18.3

7.4

67.0

65.3



Recycled Pt ZIF-67/Zeolite 5A Fresh Pt ZIF-67/Zeolite 5A Recycled Pt ZIF-67/Zeolite 5A

N2

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98.3

0.6

0.4

0.3

0.4

0.4

3.4

55.5

24.1

14.9

55.5

54.6

97.3

5.5

5.6

3.9

3.5

3.5

7.8

60.0

0.0

10.2

60.0

58.4

95.2

5.3

5.5

3.4

3.0

2.9

8.7

57.3

0.0

13.8

57.3

54.6

Figure 1. ATR-FTIR spectra of (a) linoleic acid, and liquid products under reaction gases (b) CO2, (c) CO2 recycle, (d) N2, (e) N2 recycle, (f) H2, (g) H2 recycle.

When the reaction was carried out in the presence of nitrogen, heptadecane yield as high as 58.4% was observed. Nitrogen products showed very high decarboxylation, nearly complete deesterification, and complete saturation, but accumulated a large amount of short hydrocarbons. The saturation of fatty acid products under inert gases has been observed and described by Morgan et al.37 Decarboxylation was the main reaction pathway, indicated by the absence of C18


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products.21 As compared to the reaction under hydrogen atmosphere, nitrogen resulted in only a ~4% decrease in catalytic activity.

In the presence of carbon dioxide, heptadecane yields were 63.5 and 63.1% for fresh and recycled catalyst respectively, resulting in under 1% loss in activity. Under carbon dioxide atmospheres, the selectivity to heptadecane was the highest resulting in less short hydrocarbons and no C18 products, indicating decarboxylation was the main reaction pathway.21 The products were completely saturated but contained some remaining acids and esters giving a lower conversion (88.2 and 78.3%). This was corroborated by the ATR-FTIR spectra. In the absence of hydrogen, Xing et. al38 have suggested that the source of hydrogen comes from H2 release during the formation of cracked products. Specifically, the authors suggest that CO2 is consumed in an oxidative dehydrogenation (ODH) reaction with C3H8 that follows the following mechanism: + 3"# → 6" + 4# allowing hydrogenation of the alkenes. Compared to our previous

results, we have observed a decrease in yield as the degree of unsaturation in the fatty acid increases.2,21 Specifically, heptadecane yield in carbon dioxide atmospheres for monounsaturated oleic acid (18:1) was 90.5%.21 For saturated palmitic and lauric acids the yield for the corresponding decarboxylation product was 92 and 94%, respectively.2 This comparison suggests that the yield to heptadecane decreases as the degree of unsaturation increases, which agrees well with previous literature for other catalytic systems.31,32,35

3.2 Catalyst Composition, Stability, and Recyclability As shown in our previous studies, Pt/ZIF-67/Zeolite 5A catalysts displays good chemical and thermal stability.2,4,21 In this work, our catalysts also displayed enhanced stability when linoleic



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acid was the reactant. Fresh Pt/ZIF-67/Zeolite 5A was found to have a Pt loading of 0.30 wt% by ICP analysis (Table S4). The crystalline structure of the catalyst was preserved when exposed to all three gases after reaction and regeneration evidenced by the XRD patterns (Figure 2). The TGA profiles (Figure 3) confirm that the catalysts were very stable up to 350°C after which, ZIF-67 tends to degrade.39 Mass loss up to 250°C was attributed to free and entrained water.40

Figure 2. XRD patterns of (a) zeolite 5A beads, (b) fresh Pt/ZIF-67/Zeolite 5A bead with 2 layers, (c) recycled catalyst—CO2, (d) recycled catalyst—N2, (e) recycled catalyst—H2.


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Figure 3. TGA profiles of (a) recycled catalyst—CO2, (b) fresh Pt/ZIF-67/Zeolite 5A bead with 2 layers, (c) recycled catalyst—N2, (d) recycled catalyst—H2.

The thickness of the ZIF-67 layers grown on 5A beads were estimated by image analysis from the FE-SEM. Representative micrographs of the beads show that the layer size was consistent among the fresh and spent beads as shown in Figure 4. Specifically, the average ZIF-67 layer thickness was ~245 µm for the fresh catalyst and ~209, ~275, and ~201 µm for the spent catalysts under CO2, N2, and H2, atmospheres, respectively. The structural quality of the layer could be attributed in part to the low temperature range required for the hydrothermal ZIF-67 synthesis, avoiding large thermal expansion coefficient mismatching between the zeolite and the ZIF.41 Figure S1 shows typical digital pictures of the ZIF-67/Zeolite 5A beads and the Pt/ZIF67/Zeolite 5A beads after impregnation of tetraamine-platinum nitrate. BET surface areas decreased slightly after one reaction from 553±1 for fresh Pt/ZIF-67/Zeolite 5A to 477±2, 438±1, and 495±3 for hydrogen, nitrogen, and carbon dioxide reactions, respectively. The decrease in surface area correlates with the slight decrease in heptadecane yield for the spent catalysts (Table 1) and the decrease in platinum on the catalyst. Spent H2, CO2, and N2 catalysts had a Pt 10 ACS Paragon Plus Environment


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loading of 0.26, 0.24, and 0.20wt% (Table S4). Specifically, the decrease in heptadecane yield was minimum for the spent catalyst under CO2 which was the catalyst with the smallest decrease in surface area, and modest Pt leaching. The decrease in surface area for the spent catalysts could be attributed to the formation of surface carbon deposited during the decarboxylation reaction.4 Previously, we demonstrated that the presence of CO2 promoted carbon removal generated and deposited at the catalysts surface during the deoxygenation of oleic acid.21 In principle, this would keep cleaner the catalyst surface, leading to a minimum decrease in selectivity. The thermal stability of the catalyst is limited to ~350°C, and under typical industrial settings, hot spots could potentially compromise the catalyst stability. Overall, the spent catalysts displayed only a slight decrease in catalytic performance as compared to the fresh catalysts, indicating chemical stability after the reaction. a

b


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c

d

Figure 4. Representative FE-SEM images of (a) fresh Pt/ZIF-67/Zeolite 5A bead with 2 layers, (b) recycled catalyst—CO2, (c) recycled catalyst—N2, (d) recycled catalyst—H2.

3.3 Correlations for ATR-FTIR and titrimetric analyses Technical grade linoleic acid was evaluated by GC-MS and ATR-FTIR (from here on referred to as FTIR). The composition was found to be 69% linoleic acid, 22% oleic acid, 3% palmitic acid, and 5% other unidentified species from GC-MS. From the FTIR spectrum it is hypothesized that some esters were present in the sample evidenced by the peak shouldering at 1740 cm-1 (Figure 1). Esters were found in products from the carbon dioxide reactions (Figure 1). When deoxygenating linoleic acid, difficulty in identifying esters and unsaturated fatty acids is attributed a wide variety of complex bond configurations which occur at similar molecular weights, lending to difficult identification by common GC-MS libraries and standards.30–32 Linoleic acid has 56 possible conjugated isomers which cannot be sufficiently separated by GCMS alone.42 Because these acids in the final products are often difficult to identify, many researchers rely on the calculation of conversion by percent decarboxylation from either the FTIR stretch area at 1707 cm-1 or the acid value test.2,4,21,43–45 In our case, esters were observed in the reactants and the products, making this analysis insufficient in calculating total conversion.



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To better quantify the presence of esters, the ester value of linoleic, oleic, and stearic acid was calculated by first finding the saponification value of each acid, and in turn calculating the ester value by Equation 1. These ester values were compared to the associated FTIR stretch at 1740 cm-1. In solutions dominated by carboxylic acids, the ester stretch at 1740 cm-1 resulted in shouldering of the carboxylic acid peak, and required deconvolution (Figure S2). The ester peak area was correlated with the titrimetric ester value and showed good agreement (Figure 5A). This regression was used to calculate the ester value of the products. Ester values were not evaluated by titrimetric analysis in the products as insufficient sample remained after acid value, GC-MS, and FTIR testing. Once the ester values and acid values of the products and reactants were known, the overall conversion could be calculated by Equation 2. As shown in Figure 5B, titrimetric analysis of the acid value also resulted in strong correlations with FTIR peak areas for the pure acids and the products. The beneficial effect of Co as promoter or co-catalyst for hydrodeoxygenation and decarboxylation reactions is well documented. For instance, Centeno et al. reported the use of Co-noble metal based catalysts for the hydrodeoxygenation reaction of different model molecules containing carbonyl, carboxyl, hydroxyl and methoxy groups.26 These authors found that the presence of Co favored the decarboxylation activity. A synergistic effect between the noble metal and Co was responsible for this catalytic behavior. Wang et al. attributed also a positive synergistic effect when Co was incorporated into Mo based catalysts for an enhanced catalytic activity for hydrodeoxygenation of bio-oils. Furthermore, cobalt-based catalysts enhance the C(sp2)- O cleavage via direct deoxygenation pathway.24 Our group also has reported the beneficial effect of Co (as ZIF-67) for the decarboxylation of oleic acid to heptadecane.4


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Figure 5. ATR-FTIR areas for linoleic acid (◇), oleic acid (□), stearic acid (△), and liquid products (○) compared with (a) ester values, and (b) acid values.

3.4 Comparison to the State-of-the-Art Catalysts for Deoxygenation of Linoleic Acid Table 2 summarizes the performance of different catalysts reported for the deoxygenation of linoleic acid to heptadecane. The highest heptadecane yield from linoleic acid, reported by Besse et al., was 83%.22 Their catalyst system consisted of 2wt% Pt/C with ethanol and water (1:1). Ethanol was employed as a hydrogen-donor co-solvent to promote hydrogenation. Their reaction parameters were 350°C, 220 bar, 6 h.22 Our best catalysts displayed heptadecane yields in the ~61-68% range. However, we employed milder reaction conditions (lower pressure, temperature, and reaction time). Furthermore, our noble metal loading was only 0.3wt%. When considering feasible reaction conditions for industrial scale-up, reviews of current technology agree that high pressure is a key drawback for catalyzed biofuel production.46,47 Overall, the 0.3wt% Pt/ZIF67/Zeolite 5A system gave high heptadecane yields considering the low noble metal loading and moderate reaction conditions. Table 2. Comparison of the catalytic conversion of linoleic acid to heptadecane over state-of-the art catalysts. Best catalytic performance is shown. XTOT=conversion; SC17=selectivity to heptadecane; YC17= yield to heptadecane 14 ACS Paragon Plus Environment


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SC17 (%)

YC17 (%)

3

14.5

0.4

1:100

87

50.6

44

T = 350°C, t = 2 h , H2O

1:115

80

18.8

15

2wt% Pt/C

T = 350°C, t = 6 h, P = 220 bar, 1:1 EtOH: H2O

1:160

99

84

83

32

5% Pt/C

T = 330°C, t = 2.5 h, H2O

1:200

97

5.2

5

31

5% Pd/C

T = 300°C, t = 6 h, P = 15 bar (5% H2 in Ar)

1:460

34

3

1.0

This 0.3wt% Pt/ZIF-67/ work zeolite 5A

T = 320°C, t = 2 h, P = 20 bar (CO2)

1:333

88.2

72.0

63.5


T = 320°C, t = 2 h, P = 20 bar (H2)

1:333

97.4

67.0

65.3


T = 320°C, t = 2 h, P = 20 bar (N2)

1:333

97.3

60.0

58.4

Reaction conditions

Noble metal to XTOT linoleic acid (g:g) (%)

Ref

Catalyst

33

1wt% Pd/C (mesoporous) T = 300°C, t = 6 h, P = 6 bar (1% H2 in Ar)

1:30

34

3wt% Pt/C (mesoporous) T = 330°C, t = 3 h, tetradecane

35

5wt% Pt3Sn/C

22

4. Conclusions In summary, linoleic acid was saturated and deoxygenated in the presence of hydrogen, carbon dioxide, and nitrogen over 0.3wt% Pt/ZIF-67/Zeolite 5A catalysts. Heptadecane yield via decarboxylation was as high as 63.5%, 65.3%, and 58.4% when carbon dioxide, hydrogen, and nitrogen were used during the reaction, respectively. In the presence of hydrogen, hydrodeoxygenation was a competing pathway to decarboxylation. Carbon dioxide and nitrogen atmospheres resulted in the lowest loss of activity, ~1% and ~4%, respectively. We found good fitting correlations when comparing FTIR spectral data to commonly used titrimetric acid and ester value tests. These correlations could alleviate significant time spent on titration, and decrease the use of expensive chemicals needed for titration experiments. The zeolite-supported, Pt-dispersed, metal organic framework catalyst system presented here is promising for the deoxygenation of saturated, mono, and polyunsaturated fatty acids to liquid fuel range


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hydrocarbons. In particular these catalysts display high heptadecane yields at moderate reaction conditions. Supporting Information This material is available free of charge via the Internet at http://pubs.acs.org. Digital pictures of the ZIF-67/Zeolite 5A beads, and Pt/ZIF-67/Zeolite 5A beads after impregnation of tetraamine-platinum nitrate. Additional FTIR spectra for stearic, oleic, and linoleic acids, ICP of fresh and spent catalysts, addition liquid distribution data. AUTHOR INFORMATION Corresponding Author Moises A. Carreon, [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources National Science Foundation NSF-CBET Award # 1705675 Notes The authors declare no competing financial interests. Acknowledgements M.A. Carreon thanks National Science Foundation NSF-CBET Award # 1705675 for financial support of this work. Additionally, we thank Professor Jim Ranville and Rachel Mizenko, Colorado School of Mines, Chemistry Department for their assistance with ICP-AES analysis.

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Decarboxylation of Diunsaturated Linoleic Acid to Heptadecane over

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