Three Pd/H-CHA samples were prepared containing 53.0 %, 10.8 % and 6.5 % paired Al sites at near fixed Si/Al ratio and similar Pd loading. According to H2 temperature-programmed reduction, Pd was present almost exclusively as isolated cations in the two samples containing the higher concentrations of paired Al sites, whereas in the other sample PdO was also present. Simulated lean cold start tests on the fresh samples conducted in a microflow reactor showed that the sample containing PdO stored the lowest amount of NOx. When tested with CO/H2, the sample containing 53.0 % paired Al sites showed significantly better storage capacity than the other samples and deactivated less rapidly upon sequential tests. Experiments using lean gasoline engine exhaust revealed similar trends. This study showed that a high concentration of paired Al sites in Pd/H-CHA is beneficial for NOx storage capacity, thermal durability, and minimizing deactivation in the presence of CO/H2.

Although renewable energy sources like solar and windprovide alternativesto fossil fuels for electricity generation, liquid transportationfuels are still required for marine and aviation travel, the electrificationof which remains years or decades away. For these applications, biofuelsproduced through the deoxygenation of biomass provide a viable alternative.To elucidate the mechanism behind the deoxygenation of oleaginousbiomass to hydrocarbons via decarbonylation (DCN), this work presentsa joint experimental and computational investigation wherein propanoicacid (PAc) and a Ni[111] surface were used to model fatty acids andNi-based catalysts. Diffuse reflectance infrared Fourier transformspectroscopy (DRIFTS) measurements show the binding mode of PAc onNi/Al2O3 to be predominantly bidentate, whichinformed density functional theory (DFT) studies. The bidentate adsorptionmode of PAc plays a key role in determining the DCN mechanism since & alpha;-carbon dehydrogenation of PAc was deemed unfeasible, in contrastwith previous reports. A mean-field microkinetic model reveals thefollowing dominant pathway at 573 K: PAc dehydroxylation affords aCH(3)CH(2)CO* intermediate that after two & alpha;-carbondehydrogenation steps forms CH3CCO*, which then undergoesCO abstraction and hydrogenation to ultimately yield ethane. The overallreaction has a turnover frequency (TOF) of 2.75 x 10(-11) s(-1), with the dehydroxylation of CH3CH2COOH* being the rate-determining step with a degreeof rate control of one. The apparent activation barrier determinedhere is much lower than that previously reported, which could be dueto the binding mode of PAc and considered experimental conditions.The effect of partial pressures of gaseous intermediates on the overallrate of reaction showed a negative order with respect to H-2 partial pressure, while a positive order was observed with respectto PAc partial pressure. Overall, this work shows the importance ofexperimentally determining the binding mode of carboxylic acids onthe catalyst surface to inform DFT work designed to elucidate theDCN reaction mechanisms.

The incomplete reduction and poor dispersion of Ni sites restrict the catalytic performance of Ni catalysts in the decarboxylation/decarbonylation (DCX/DCN) of triglycerides to fuel-like hydrocarbons. In this study, by employing Pd as promoter and/or using multifunctional supports, the activity of Ni catalysts in tristearin deoxygenation was greatly improved. Notably, 25%Ni/Al2O3 and 0.75%Pd/Al2O3 displayed conversion values <= 2%. In contrast, 25%Ni-0.75%Pd/Al2O3 afforded 100% conversion, 100% yield of diesel-like hydrocarbons and a selectivity to C17 - the main product of DCN/DCX - of 67%. The fact that the performance of the Ni-Pd catalyst is vastly superior to that of the corresponding monometallic formulations is clearly indicative of a promotion effect resulting from the interaction between the two metals. Pd addition promoted Ni reduction, thereby increasing the number of active sites. The effect of different supports (Al2O3, SiO2-Al2O3, ZrO2, and Ce0.8Pr0.2O2) of Ni-Pd catalysts were studied, and the use of SiO2-Al2O3 was observed to enhance catalyst performance by further promoting Ni reduction as well as through its high surface area and strong acidity. Moreover, using SiO2-Al2O3 as the support partially changes the deoxygenation pathway from DCX/DCN to hydrodeoxygenation, which is attributed to the ability of strong acid sites to catalyze the dehydrogenation of an alcohol intermediate to the corresponding alkene. (C) 2022 Elsevier Ltd. All rights reserved.

Several technologies have been developed to produce sustainable aviation fuel (SAF), the hydroprocessing of esters and fatty acids (HEFA) representing one of the most mature pathways. Although HEFA has been widely adopted by industry, this pathway is mainly reliant on the hydrodeoxygenation (HDO) reaction, which requires large amounts and high pressures of hydrogen gas that reduces the cost-effectiveness of the process. In this study, the economic, environmental, and exergy analyses of two alternative scenarios for the catalytic production of SAF were considered. In both scenarios, SAF is produced through the catalytic deoxygenation of tall oil fatty acid (TOFA) via decarboxylation/decarbonylation (deCOx) - an approach requiring smaller amounts and lower pressures of hydrogen, feedstocks of lower purity and cost, and simpler supported metal catalysts relative to HDO. The material and energy balance was calculated using Aspen Plus process simulation software. Scenario 1 comprises a plant in which the catalytic deoxygenation of TOFA via deCOx is performed using hydrogen gas obtained commercially, while scenario 2 integrates catalytic deoxygenation with a plant that produces hydrogen gas via hydrothermal gasification. The study revealed that both scenarios were economically feasible relative to other pathways for SAF production, with the minimum fuel selling price (MFSP) of scenario 2 (USD$ 0.39/L) being lower than that of scenario 1 (USD$ 0.62/L). In addition to being the most economically viable, scenario 2 was also found to be preferable from an environmental standpoint since it also shows a lower global warming potential (GWP). Discounted cash flow analysis (DCFA) was used to determine other economic indicators such as net present value (NPV), internal rate of return (IRR), net rate of return (NRR) and payback period (PBP), which was estimated to be approximately 3 years for both scenarios. Finally, sensitivity analysis confirms that the raw materials and equipment purchase costs have the greatest impact on the MFSP.

Current vehicles generate a large fraction of their total tailpipe emissions during the beginning of the cold start test. For a current 3.5L GTDI (gasoline turbocharged direct injection) production vehicle, the majority (>60%) of CO, HC, and NOx are emitted in the first 60 seconds before the three-way catalyst reaches operating temperature of 350°C. Clearly, a means of storing HC and NO during cold starts would have a meaningful, measurable impact on vehicle tailpipe emissions. Against this background, this project aimed to develop fundamental understanding of the chemistry of NO/HC adsorption and reaction in Pd-zeolites so as to facilitate the rational design of passive NOx adsorber (PNA) catalysts. Given that numerous publications exist concerning HC trapping by Pd-zeolites, emphasis was placed on identifying the factors controlling NOx adsorption in Pd-zeolites. The approach adopted combined both experimental and computational methods, which together allow a deeper understanding of the governing chemistry than the use of either method alone. The workflow began with Pd/H-CHA and Pd/H-BEA catalyst synthesis and characterization, in which the Si/Al ratio and extent of Al pairing were systematically varied. This was followed by catalyst evaluation using temperature-programed adsorption/desorption methods, as well as in situ diffuse reflectance UV-vis spectroscopy (DRUVS), X-ray absorption near edge spectroscopy (XANES), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission IR spectroscopic measurements to probe the nature of the NO adsorption sites and the form of the adsorbed NO. In parallel, the adsorption of NO and other relevant species (H2O, CO, HCs) was studied by means of quantum chemical calculations in order to rationalize the experimental data and provide additional insights. Catalyst aging studies were also performed with the aim of elucidating the mechanism(s) of catalyst degradation. Finally, the insights gained in this project were applied to the preparation of an optimized PNA catalyst, the performance of which was validated using exhaust gas from an engine dynamometer. Key findings included the observation that the dominant mechanism of formation for ion-exchanged Z2Pd and Z[PdOH] species in Pd-CHA is solid-state ion-exchange, and Z2Pd species are likely the most thermodynamically stable ion-exchanged structure after air treatments (>400 °C). CO-DRIFTS showed the presence of Pd+-CO bands at low Pd loadings on Pd-BEA with increasing Pd2+ content at higher loadings. Reduction of ionic Pd and PdO species by H2 was found to generate large quantities of small, pore-confined Pd metal particles, H2-TPR experiments showing that Pd-CHA has a greater ability to maintain Pd in an ionic state than does Pd-BEA and achieves complete recovery of ionic Pd species by re-oxidation treatments regardless of the reductant employed. However, reduction in CO was shown to produce larger Pd metal particles than reduction in H2; moreover, a lower degree of Pd re-dispersion upon re-oxidation was also observed for CO-reduced Pd-BEA compared to the corresponding H2-reduced sample. Quantum mechanical calculations showed that ionically dispersed Pd species (Pd+ and Pd2+) are thermodynamically most favorable in Pd-CHA over a wide range of oxidizing and reducing conditions. Calculated Gibbs free energies for NO adsorption show that NO generally binds more strongly on Pd+ sites than on Pd2+ sites, suggesting that the former are responsible for the high-temperature desorption peak observed in TPD experiments, while the latter contribute to the observed low-temperature feature. When evaluated in simulated exhaust gas, the presence of reductants (C2H4, C3H6, CO/H2) improved the NOx storage performance of Pd/zeolite passive NOx adsorbers under lean conditions but not stoichiometric conditions and mitigated the inhibitory effects of water. Against this, repeated cold start tests showed progressive decline in NO storage capacity, which could be linked to facile reduction of Pd by CO and H2O. For CHA, increasing the percentage of paired Al sites in the zeolite was beneficial for improving robustness to repeated cold starts and improved thermal durability. However, the low intrinsic storage efficiency (at best 1 NO per Pd) and the continuing high cost of palladium, along with remaining durability challenges, create an unfavorable business case for implementing Pd/zeolite passive NOx adsorbers on vehicles at the current time.

The structure and evolution of Pd species in Pd-exchanged zeolite materials intended for use as passive NO x adsorbers were examined under various pretreatment conditions. Using in situ CO-diffuse reflectance infrared spectroscopy, Pd structures were characterized after 500 °C pretreatments in inert (Ar), water (1-2% H2O in Ar), oxidizing (air), and reducing (H2, CO) atmospheres. Two zeolites of similar Si/Al ratios but different framework topologies (Beta, CHA) were found to show different distributions of Pd species, depending on the reducing agent used. Reduction in H2 (500 °C; 10% H2 in Ar) followed by re-oxidation (500 °C; air) led to higher amounts of single-site Pd ions on Pd-CHA than Pd-Beta, whereas high-temperature reduction in CO (500 °C; 1000 ppm CO in Ar) followed by re-oxidation (500 °C; air) led to significant loss of ionic Pd on both Pd-CHA and Pd-Beta, albeit H2 temperature-programmed reduction and XPS experiments suggest that this phenomena may be limited to surface Pd. High-temperature treatments with water (500 °C; 1-2% H2O in Ar) are shown to form either Pd metal or PdO particles, with Pd-Beta being more susceptible to these effects than Pd-CHA. This work suggests that the effects of CO are especially problematic with respect to the durability of these materials in passive NO x adsorption applications, especially in the case of Beta zeolite.

Inexpensive Ni-based catalysts can afford comparable performance to costly precious metal formulations in the conversion of fat, oil, or greases (FOG) to fuel-like hydrocarbons via decarboxylation/decarbonylation (deCOx). While the addition of certain metals has been observed to promote Ni-based deCOx catalysts, the steady-state performance of bimetallic formulations must be ascertained using industrially relevant feeds and reaction conditions in order to make meaningful comparisons. In the present work, used cooking oil (UCO) was upgraded to renewable diesel via deCOx over Ni/Al2O3 promoted with Cu, Fe, or Pt in a fixed-bed reactor at 375 °C using a weight hourly space velocity (WHSV) of 1 h−1. Although all catalysts fully deoxygenated the feed to hydrocarbons throughout the entire 76 h duration of these experiments, the cracking activity (and the evolution thereof) was distinct for each formulation. Indeed, that of the Ni-Cu catalyst was low and relatively stable, that of the Ni-Fe formulation was initially high but progressively dropped to become negligible, and that of the Ni-Pt catalyst started as moderate, varied considerably, and finished high. Analysis of the spent catalysts suggests that the evolution of the cracking activity can be mainly ascribed to changes in the composition of the metal particles.

This contribution describes an algal fractionation scheme based on cell lysing and carbohydrate hydrolysis under acidic conditions, coupled with solvent extraction, that produces algal lipids, carbohydrates, and proteinaceous solid from partially dewatered algal biomass. A design of experiments analysis was employed to identify the effect of fractionation conditions on the yields of the three product streams. By selection of appropriate conditions, the process can be steered from simple lipid extraction to near complete fractionation of the biomass. Lipid purification and upgrading were respectively achieved with a low-cost adsorbent and an inexpensive Ni-based catalyst that deoxygenated the lipids via decarboxylation/decarbonylation, an approach offering several advantages over the hydrodeoxygenation-based processes typically employed to convert lipids to hydrocarbons. The proteinaceous solids obtained were found to have much lower ash content as well as higher protein content relative to the untreated algae, enhancing the suitability of this material as a feedstock for the production of bioplastics.

This project sought to address the technical and economic barriers to carbon dioxide (CO2) capture and utilization using microalgae. Specifically, a dual photobioreactor (PBR)/open raceway pond (ORP) cultivation system was evaluated with respect to capital and operational costs, productivity, and culture health, and compared to an ORP-only cultivation system. In the dual (or “hybrid”) system, a cyclic flow PBR was used to provide inoculum for two open raceway ponds after each harvest, with the hypothesis that this PBR + pond system should result in improved performance compared to traditional raceway ponds. Two other raceway ponds were operated conventionally as a control, the experiments being performed at Duke Energy’s East Bend Station in northern KY using coal-derived flue gas as the CO2 source. Although algae productivity achieved was mediocre due to the fact that the experiments had to be performed late in the growing season when climatic conditions were not optimal for high growth, the hybrid cultivation system showed a higher level of algae productivity (statistically significant) compared to the traditional ponds. In order to realize the maximum value of the algal biomass produced, fractionation of the biomass was examined. Bioplastic compounding and material characterization was subsequently performed using three feed stocks: whole biomass, lipid-extracted biomass and the proteinaceous residue from full fractionation. In general, the whole and lipid-extracted biomass gave similar results in terms of the properties of the resulting bioplastics, while the proteinaceous residue showed promise for the production of a polybutylene adipate terephthalate (PBAT) blend. Finally, sustainability assessment of a putative biorefinery system was conducted, including techno-economic and life cycle impact assessment. Nine different production scenarios were considered, comprising combinations of the three different biomass growth architectures (ORP, PBR and dual PBR-ORP systems) coupled with three different algae biomass processing pathways (drying only, lipid extraction and fractionation). Results show that the minimum selling price of the bioplastic feed stock (BPFS) is within the realm of economic competition with prices as low as $970 USD tonne-1. Additionally, life cycle impact assessment results indicate drastic improvements in performance of the produced BPFS, with reductions in greenhouse gas emissions ranging between 67 and 116% compared to a petroleum based plastic feedstock.

In order to assess the utility of fluid catalytic cracking (FCC) for upgrading bio-oils derived from the hydro thermal liquefaction (HTL) of microalgae, 10 wt% HTL algae bio-oil was blended with heavy vacuum gas oil (HVGO) and co-processed in a Short Contact Time Microactivity unit. Compared to pure HVGO, addition of 10 wt% HTL algae bio-oil caused a modest decrease in conversion at all catalyst-to-oil ratios, with marginally increased catalyst coking being observed for the blended feed. The resulting liquid products contained a higher percentage of decant oil (DCO) and a lower percentage of gasoline than those obtained when HVGO alone was employed as feed, the amount of light cycle oil (LCO) being similar in both cases. Nearly complete heteroatom removal from the blended feed was observed, the extent of denitrogenation achieved being particularly note-worthy given that nitrogen-bearing compounds are much more abundant in algae-derived bio-oils than in HVGO. Overall, results indicated that while 10% bio-oil in HVGO would be economically unfavorable when compared to upgrading HVGO alone, it is nonetheless amenable to co-processing and may offer advantages over pyrolysis oils as an FCC feed. Finally, additional means to optimize the commercial application of this process are proposed based on techno-economic considerations.

Pt represents an effective promoter of supported Ni catalysts in the transformation of tristearin to green diesel via decarbonylation/decarboxylation (deCOx), conversion increasing from 2% over 20% Ni/Al2O3 to 100% over 20% Ni-0.5% Pt/Al2O3 at 260 °C. Catalyst characterization reveals that the superior activity of Ni-Pt relative to Ni-only catalysts is not a result of Ni particle size effects or surface area differences, but rather stems from several other phenomena, including the improved reducibility of NiO when Pt is present. Indeed, the addition of a small amount of Pt to the supported Ni catalyst dramatically increases the amount of reduced surface metal sites, which are believed to be the active sites for deCOx reactions. Further, Pt addition curbs the adsorption of CO on the catalyst surface, which decreases catalyst poisoning by any CO evolved via decarbonylation, making additional active sites available for deoxygenation reactions and/or preventing catalyst coking. Specifically, Pt addition weakens the Ni-CO bond, lowering the binding strength of CO on surface Ni sites. Finally, analysis of the spent catalysts recovered from deCOx experiments confirms that the beneficial effect of Pt on catalyst performance can be partially explained by decreased coking and fouling.

While commercial hydrodeoxygenation (HDO) processes convert fats, oils, and grease (FOG) to fuel-like hydrocarbons, alternative processes based on decarboxylation/decarbonylation (deCO(x)) continue to attract interest. In this contribution, the activity of 20% Ni-5% Cu/Al2O3 in the deCO(x) of waste free fatty acid (FFA)-based feeds-including brown grease (BG) and an FFA feed obtained by steam stripping a biodiesel feedstock-was investigated, along with the structure-activity relationships responsible for Ni promotion by Cu and the structural evolution of catalysts during use and regeneration. In eight-hour experiments, near quantitative conversion of the aforementioned feeds to diesel-like hydrocarbons was achieved. Moreover, yields of diesel-like hydrocarbons in excess of 80% were obtained at all reaction times during a BG upgrading experiment lasting 100 h, after which the catalyst was successfully regenerated in situ and found to display improved performance during a second 100 h cycle. Insights into this improved performance were obtained through characterization of the fresh and spent catalyst, which indicated that metal particle sintering, alloying of Ni with Cu, and particle enrichment with Cu occur during reaction and/or catalyst regeneration.

Pd-promoted ZrO2 and WO3-ZrO2 (W-Zr) were investigated for low temperature NOx adsorption and release. Pd-promoted W-Zr exhibited high NOx storage efficiency at short storage times, subsequently releasing similar to 95% of the stored NOx upon thermal ramping to 350 degrees C. DRIFTS studies demonstrated that Pd increased nitrate formation relative to nitrite during NOx storage on both Pd-Zr and Pd-W-Zr. Moreover, Pd sites on Pd-W-Zr played a major role in NOx storage, the ad-species being readily removed by 350 degrees C. From NO- and CO-DRIFTS data, it is inferred that Pd on the acidic W-Zr support was present as mainly cationic species, and was therefore able to adsorb NO, whereas on ZrO2 Pd was not able to directly store NOx. Co-feeding CO with NO resulted in increased NOx storage capacity for Pd-W-Zr, which on the basis of DRIFTS measurements is attributed to the formation of Pd2+ (CO)(NO) complexes.

A novel cyclic flow photobioreactor, designed for the capture and recycle of CO2 using microalgae, was deployed at a coal-fired power plant. Scenedesmus acutus was cultured continuously for a four-month period, during which a biomass productivity of 0.1-0.2 g L-1 day(-1) was observed. Samples taken for DNA sequencing showed a strong correlation between the composition of the culture and environmental conditions. Dry and liquid biomass samples and the industrial fertilizers used for preparation of the nutrient medium were analyzed to determine the presence of heavy metals (As, Cd, Hg, Se) and results were compared with standardized and/or regulated maximum contaminant levels (MCLs) for metals in several possible algae derived products. Concentrations of the metals in dry algae biomass were consistent with the incorporation of metals from the supplied nutrients.

Commercial scale production of biofuels from lignocellulosic feed stocks has been hampered by the resistance of plant cell walls to enzymatic conversion, primarily owing to lignin. This study investigated whether DypB, the lignin-degrading peroxidase from Rodococcus jostii, depolymerizes lignin and reduces recalcitrance in transgenic tobacco (Nicotiana benthamiana). The protein was targeted to the cytosol or the ER using ER-targeting and retention signal peptides. For each construct, five independent transgenic lines were characterized phenotypically and genotypically. Our findings reveal that expression of DypB in the cytosol and ER does not affect plant development. ER-targeting increased protein accumulation, and extracts from transgenic leaves showed higher activity on classic peroxidase substrates than the control. Intriguingly, in situ DypB activation and subsequent saccharification released nearly 200% more fermentable sugars from transgenic lines than controls, which were not explained by variation in initial structural and non-structural carbohydrates and lignin content. Pyrolysis-GC-MS analysis showed more reduction in the level of lignin associated pyrolysates in the transgenic lines than the control primarily when the enzyme is activated prior to pyrolysis, consistent with increased lignin degradation and improved saccharification. The findings reveal for the first time that accumulation and in situ activation of a peroxidase improves biomass digestibility.

The extraction, characterization, purification and upgrading of algal lipids was examined, utilizing Scenedesmus acutus microalgae grown with flue gas from a coal-fired power plant. Lipid extraction was achieved using a procedure based on the Bligh-Dyer method, modified so as to utilize a significantly decreased solvent: biomass ratio than the original protocol. Both activated carbon and K10 montmorillonite were found to function as efficient adsorbents for the removal of chlorophyll, phospholipids and sterols from the crude algae oil. The yield of purified lipids using this approach was similar to that obtained by in situ transesterification of the lipids in S. acutus, confirming that adsorption is an effective method for the removal of non-esterifiable lipids. During the deoxygenation of the purified algae oil at 260 degrees C over a Ni-Al layered double hydroxide catalyst, deactivation of the catalyst was observed, attributed to the presence of highly unsaturated lipid chains which can act as poisons by adsorbing strongly to the catalyst surface and/or acting as precursors to coke formation. However, upgrading at 300 degrees C gave better results, the liquid product consisting of similar to 99 wt% hydrocarbons, diesel-like (C10-C20) hydrocarbons constituting 76 wt% of the liquid after 4 h on stream. (C) 2016 Elsevier Ltd. All rights reserved.

The oxidation of lignin model compounds in ionic liquid solvents was investigated as a prelude to the oxidation of lignin in these solvents where the polymer is appreciably soluble.

Molybdenum carbide was supported on three types of carbon support—activated carbon; multi-walled carbon nanotubes; and carbon nanofibers—using ammonium molybdate and molybdic acid as Mo precursors. The use of activated carbon as support afforded an X-ray amorphous Mo phase, whereas crystalline molybdenum carbide phases were obtained on carbon nanofibers and, in some cases, on carbon nanotubes. When the resulting catalysts were tested in the hydrodeoxygenation (HDO) of guaiacol in dodecane, catechol and phenol were obtained as the main products, although in some instances significant amounts of cyclohexane were produced. The observation of catechol in all reaction mixtures suggests that guaiacol was converted into phenol via sequential demethylation and HDO, although the simultaneous occurrence of a direct demethoxylation pathway cannot be discounted. Catalysts based on carbon nanofibers generally afforded the highest yields of phenol; notably, the only crystalline phase detected in these samples was Mo2C or Mo2C-ζ, suggesting that crystalline Mo2C is particularly selective to phenol. At 350 °C, carbon nanofiber supported Mo2C afforded near quantitative guaiacol conversion, the selectivity to phenol approaching 50%. When guaiacol HDO was performed in the presence of acetic acid and furfural, guaiacol conversion decreased, although the selectivity to both catechol and phenol was increased.