### Recent Submissions

• #### Silicon carbide in catalysis: from inert bed filler to catalytic support and multifunctional material

(Catalysis Reviews, Informa UK Limited, 2022-01-22) [Article]
Silicon carbide (SiC) or carborundum has unparalleled thermal stability and conductivity compared with many other materials. This feature together with its unique photoelectrical properties (tunable band gap: 2.39–3.33 eV), low thermal expansion, high strength, and good chemical and thermal stability makes it an ideal inert solid in catalysis. The evolution of methods for synthesizing SiC has also progressively endowed it with additional features at the multiscale. This review tracks the development of SiC from a secondary to a leading role material in catalysis. First, the intrinsic properties of SiC are discussed and compared with other state-of-the-art catalytic materials. The synthetic methods are systematically reviewed and compared. Then, the applications of SiC in catalysis are assessed, paying particular attention to those that involve C1 chemistry (Fischer–Tropsch Synthesis and the valorization of CO2 and CH4), photocatalysis and biomass conversion. Finally, the potential future applications of SiC are also addressed and discussed.

• #### A decoupled modeling approach and experimental measurements for pyrolysis of C6-C10 saturated fatty acid methyl esters (FAMEs)

(Combustion and Flame, Elsevier BV, 2022-01) [Article]
Biodiesels are promising renewable fuels that can aid in the transition to carbon neutrality. The high molecular weight and complex composition of real biodiesel fuels complicate development of compact kinetic models needed for engine simulations. Our group previously proposed the functional group approach (FGMech) to model real-fuel combustion based on the identification of intrinsic relationships between fuel molecular structure and model parameters. Establishing these relationships requires a database consisting of the model parameters of pure fuels for training. In this work, we selected five fatty acid methyl esters (FAMEs) as target fuels, including methyl pentanoate (MPE), methyl hexanoate (MHX), methyl heptanoate (MHP), methyl octanoate (MO) and methyl nonanoate (MN). To facilitate development of an FGMech reaction scheme, a decoupling model approach is adopted here for model construction. Lumped reaction mechanisms are developed to describe the (oxidative) pyrolysis of fuels while a detailed model is used for describing the conversion of pyrolysis intermediates. To validate the present model, pyrolysis experiments for these FAMEs are conducted in a jet-stirred reactor (JSR) at 1 atm and over 790–1120 K. Both the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC)/GC–MS are applied for measuring pyrolysis intermediates. The fuels, primary hydrocarbon and oxygenated products, secondary products including various aromatic compounds, are identified and quantified for model validation. The present model well-predicts the temperature window of fuel decomposition, and reasonably predicts the yields of most pyrolysis products under both present atmospheric conditions and high pressure conditions in literature. The agreement between the measured and predicted results indicates that the present decoupling methodology can accurately describe fuel decomposition and the evolution of intermediates under pyrolysis conditions. In addition, it is found that increasing alkyl CH2 groups in C6 to C10 FAMEs has little influence on the yields of primary oxygenated products; however, increasing yields of hydrocarbon products with increasing alkyl CH2 groups indicates that alkane chemistry becomes more important moving from MPE to MN.
• #### On the effects of CO2 atmosphere in the pyrolysis of Salicornia bigelovii

(Bioresource Technology Reports, Elsevier BV, 2022-01) [Article]
This study focuses on understanding the effects of a CO$_2$ atmosphere on the pyrolysis of $\textit{Salicornia bigelovii}$ by performing a detailed kinetic analysis and investigating the pyrolysis products. In comparison to N$_2$ pyrolysis, CO$_2$ pyrolysis increased the amounts of acids, phenols, amines/amides and N-aromatics in the bio-oil. Biochar showed a 6.5% increase in carbon and a 5.8% decrease in oxygen due to the presence of CO$_2$ in the pyrolysis atmosphere. CO$_2$ also inhibited the volatilization of certain functional groups, such as phenols, tertiary alcohols and aromatics from the biochar, and the surface area of the biochar was 12 times larger than pyrolysis in N$_2$ atmosphere. Pyrolysis in CO$_2$ led to an increase in the average apparent activation energy from 146.5 kJ mol$^{−1}$ in N$_2$ to 163.4 kJ mol$^{−1}$. The kinetic equation was found to conform to a three dimensional diffusion mechanism. Finally, the pre-exponential factor was determined for each reaction.
• #### Deep learning meets quantitative structure–activity relationship (QSAR) for leveraging structure-based prediction of solute rejection in organic solvent nanofiltration

(Journal of Membrane Science, Elsevier BV, 2022-01) [Article]
Methods for determining solute rejection in organic solvent nanofiltration (OSN) are time-consuming and expensive and still rely on wet-lab measurements, resulting in the slow development of membrane processes. OSN, similar to other membrane technologies, requires precise and comprehensive predictive models that can function on various solutes, membranes, and solvents. We present two prediction methods based on the quantitative structure–activity relationship (QSAR) using traditional machine learning (ML) and deep learning (DL) models. The partial least-squares regression model combined with the variable importance in projection and genetic algorithm achieves a slightly lower root-mean-square error score (8.04) than the DL-based graph neural network (10.40). For the first time, we visualize the effect of different solute functional groups on rejection, providing a new platform for a more in-depth investigation into the membrane–solute interactions, potentially enabling the design of membranes with improved selectivity. Our ML model is freely accessible on the OSN database website (www.osndatabase.com) for everyone.
• #### Solvent-Resistant Thin-Film Composite Membranes from Biomass-Derived Building Blocks: Chitosan and 2,5-Furandicarboxaldehyde

(ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-12-30) [Article]
To address the increasing interest in environmental issues, green and sustainable material-based membranes have attracted significant research interest with the promise to replace fossil-based membranes and to reduce waste generation. In this work, more sustainable thin-film composite (TFC) membranes are designed and fabricated via interfacial polymerization of green building blocks, namely, shrimp farming waste chitosan in the aqueous phase and plant-based 2,5-furandicarboxaldehyde in the organic phase, on an upcycled polyethylene terephthalate porous support. The TFC membranes showed excellent acetone permeance up to 12 L m–2 h–1 bar–1 with a molecular weight cutoff value of approximately 317 g mol–1. The membrane separation performance was optimized by fine-tuning the building block concentrations, which provided a new upper-bound in the plot of acetone permeance versus styrene dimer rejection. In addition, for the first time, TamiSolve was employed as a green solvent to activate the selective layer of the chitosan-based TFC membrane, resulting in a significant enhancement in the permeance of diverse pure solvents including ethanol, methyl ethyl ketone, acetone, and acetonitrile with no remarkable defects and high solute rejections. Our proposed green TFC fabrication platform enables the replacement of toxic and fossil-based solvents and reagents in developing high-performance and solvent-resistant nanofiltration membranes.
• #### Ru-Bipyridine Entrapped in the Supercages of EMC-1 Faujasite as Catalyst for the Trifluoromethylation of Arenes

(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-12-27) [Article]
Trifluoromethyl (CF3) groups are versatile structural motifs especially in the field of agrochemicals and pharmaceuticals. However, current trifluoromethylation reactions are generally associated with stoichiometric amounts of transition metals/metal oxidants, homogeneous catalysts, high temperatures, and expensive trifluoromethylating agents. In this work, the homogeneous photocatalyst Ru(bipy)32+ is entrapped in the pores of a faujasite support (EMC-1) via a "ship-in-a-bottle"strategy. The formation of the coordination compound was confirmed by Fourier transform infrared (FTIR), UV-Vis spectroscopy, and X-ray absorption spectroscopy (XAS). Due to its high stability toward acidified environments, this single-site heterogeneous catalyst is suitable for the trifluoromethylation of synthetically interesting (hetero)arenes under visible-light irradiation at room temperature. Furthermore, the heterogeneous catalyst could efficiently be reused for at least three times with minimal catalyst leaching/deactivation.
• #### High purity, self-sustained, pressurized hydrogen production from ammonia in a catalytic membrane reactor

(Chemical Engineering Journal, Elsevier BV, 2021-12-24) [Article]
The combination of catalytic decomposition of ammonia and in situ separation of hydrogen holds great promise for the use of ammonia as a clean energy carrier. However, finding the optimal catalyst – membrane pair and operation conditions have proved challenging. Here, we demonstrate that cobalt-based catalysts for ammonia decomposition can be efficiently used together with a Pd-Au based membrane to produce high purity hydrogen at elevated pressure. Compared to a conventional packed bed reactor, the membrane reactor offers several operational advantages that result in energetic and economic benefits. The robustness and durability of the combined system has been demonstrated for>1000 h on stream, yielding a very pure hydrogen stream (>99.97 % H2) and recovery (>90 %). When considering the required hydrogen compression for storage/utilization and environmental issues, the combined system offers the additional advantage of production of hydrogen at moderate pressures along with full ammonia conversion. Altogether, our results demonstrate the possibility of deploying high pressure (350 bar) hydrogen generators from ammonia with H2 efficiencies of circa 75% without any external energy input and/or derived CO2 emissions.
• #### Fructose to Sorbents: Synthesis of Metal–Organic Frameworks Directly from Biomass for Humid Shale Gas Separation

(ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-12-13) [Article]
The synthesis of metal–organic frameworks (MOFs) directly starting from biomass, making the most of renewable feedstocks and allowing for coupled or continuous processing, is intriguing. The interference of water (vapor) greatly hinders the wide utilization of MOFs in, e.g., recovering ethane from humid shale gas, which is a critical process for purifying natural gas in practical scenarios. Here, we propose a concept of direct ligand and MOF synthesis in a continuous routine, i.e., a linear synthesis of a bioderived ligand (furan-2,5-dicarboxylic acid), starting from a biomass source (fructose), followed by the in situ synthesis of a series of different MOFs. This strategy is also exempt from the tedious and energy-intensive processes of filtering, purifying, or drying intermediate products. The obtained renewable MOFs, particularly MIL-160(Al), reveal superior ethane capture abilities from shale gas mixtures under ambient conditions compared to most of the MOF materials reported to date. MIL-160(Al) also demonstrates a remarkable cycling nature and facile sorption regenerability to selectively capture ethane even under high-humidity conditions, as verified by static gas sorption measurement, experimental breakthrough tests, and in-depth theoretical studies, further conferring it with great potential for industrial applications.
• #### Molecular engineering of intrinsically microporous polybenzimidazole for energy-efficient gas separation

(Applied Materials Today, Elsevier BV, 2021-12-04) [Article]
Polybenzimidazole (PBI) is a high-performance polymer that exhibits high thermal and chemical stability. However, it suffers from low porosity and low fractional free volume, which hinder its application as separation material. Herein, we demonstrate the molecular engineering of gas separation materials by manipulating a PBI backbone possessing kinked moieties. PBI was selected as it contains NH groups which increase the affinity towards CO$_2$, increase sorption capacity, and favors CO$_2$ over other gasses. We have designed and synthesized an intrinsically microporous polybenzimidazole (iPBI) featuring a spirobisindane structure. Introducing a kinked moiety in conjunction with crosslinking enhanced the polymer properties, markedly increasing the gas separation performance. In particular, the BET surface area of PBI increased 30-fold by replacing a flat benzene ring with a kinked structure. iPBI displayed a good CO$_2$ uptake of 1.4 mmol g$^{−1}$ at 1 bar and 3.6 mmol g$^{−1}$ at 10 bar. Gas sorption uptake and breakthrough experiments were conducted using mixtures of CO$_2$/CH$_4$ (50%/50%) and CO$_2$/N$_2$ (50%/50%), which revealed the high selectivity of CO$_2$ over both CH$_4$ and N$_2$. The obtained CO$_2$/N$_2$ selectivity is attractive for power plant flue gas application requiring CO$_2$ capturing materials. Energy and process simulations of biogas CO$_2$ removal demonstrated that up to 70% of the capture energy could be saved when iPBI was used rather than the current amine technology (methyl diethanolamine [MDEA]). Similarly, the combination of iPBI and MDEA in a hybrid system exhibited the highest CO$_2$ capture yield (99%), resulting in nearly 50% energy saving. The concept of enhancing the porosity of PBI using kinked moieties provides new scope for designing highly porous polybenzimidazoles for various separation processes.
• #### Production of Linear Alpha Olefins via Heterogeneous Metal-OrganicFramework (MOF) Catalysts

(2021-12) [Dissertation]
Committee members: Pinnau, Ingo; Castaño, Pedro; Huang, Kuo-Wei; Yan, Ning
Linear Alpha Olefins (LAOs) are one of the most important commodities in the chemical industry, which are currently mainly produced via homogenous catalytic processes. Heterogeneous catalysts have always been desirable from an industrial viewpoint due to their advantages of low operation cost, ease of separation, and catalyst reusability. However, the development of highly active, selective, and stable heterogeneous catalysts for the production of LAOs has been a challenge throughout the last 60 years. In this dissertation, we designed and prepared a series of heterogeneous catalysts by incorporating structural moieties of homogenous benchmark catalysts into metal-organic-frameworks (MOFs), aiming to provide a feasible solution to this long-standing challenge. First, we reviewed the background and state of the art of this field and put forward the main objectives of our research. Then, we thoroughly discussed a novel heterogeneous catalyst (Ni-ZIF-8) that we developed for ethylene dimerization to produce 1-butene, focusing on its designed principle, detailed characterizations, catalytic performance evaluation, and reaction mechanisms. Ni-ZIF-8 exhibits an average ethylene turnover frequency greater than 1,000,000 h$^{-1}$ (1-butene selectivity >85%), far exceeding the activities of previously reported heterogeneous and many homogenous catalysts under similar conditions. Compared with homogenous nickel catalysts, Ni-ZIF-8 has significantly higher stability and showed constant activity during four hours of continuous reaction for at least two reaction cycles. The combination of isotopic labeling studies and Density Functional Theory calculations demonstrated that ethylene dimerization on Ni-ZIF-8 follows the Cossee-Arlman mechanism, and that the full exposure and square-planer coordination of the nickel sites account for the observed high activity. After that, we further optimized the Ni-ZIF-8 catalytic system from the perspective of practical applications. We achieved double productivity of 1-butene by optimizing the synthetic conditions and explored its usability and performances under solvent-free conditions. Then, we extended our catalyst design concept to prepare heterogeneous catalysts comprising other metals and MOFs, which provided a suitable platform for studying the effects of the metallic center and coordination environment on the catalytic production of LAOs. Finally, we gave our perspectives on the further development of heterogeneous catalysts for the production of LAOs.
• #### Tailored Pore Size and Microporosity of Covalent Organic Framework (COF) Membranes for Improved Molecular Separation

(Journal of Membrane Science Letters, Elsevier BV, 2021-12) [Article]
Three highly crystalline truxene-based β-ketoenamine COF membranes (TFP-HETTA, TFP-HBTTA and TFP-HHTTA) are fabricated via a de novo monomer design approach to understand the fundamental correlations between pore structure and molecular separation performance. By introducing bulky alkyl groups into the truxene framework, the pore size of TFP-HETTA, TFP-HBTTA, and TFP-HHTTA are systematically tuned from 1.08 to 0.72 nm. Accordingly, the TFP-HETTA showed good water permeance of 47 L m−2 h−1 bar−1 along with a prominent rejection rate of Reactive Blue (RB, 800 Da) but less than 10% rejection rate of inorganic salts. In contrast, the TFP-HHTTA membrane with pore size of 0.72 nm can reject small dye molecules (SO, 350 Da) and trivalent salts but with a moderate water permeance of 19 L m−2 h−1 bar−1. The pore-flow model rooted from the viscous flow could well fit the observed organic solvent nanofiltration results of all three COF membranes.
• #### Facile suppression of intensified plasticization in glassy polymer thin films towards scalable composite membranes for propylene/propane separation

(Journal of Membrane Science, Elsevier BV, 2021-12) [Article]
Membrane-based propylene/propane (C3H6/C3H8) separation has the potential to significantly reduce the extremely high energy consumption in the conventional distillation process. However, no large-scale commercialization case currently exists despite decades of remarkable advancements in membrane materials. This challenge can potentially be attributed to a lack of understanding of the close relationship between material properties and membrane configurations, including confinement-driven transitions in polymer dynamics from the bulk to thin films (<1 μm). We first report design aspects of thin-film composite (TFC) membranes for C3H6/C3H8 separation based on a cost-effective, versatile, and scalable fabrication method. An unprecedented acceleration in C3 hydrocarbon-induced plasticization is observed in TFC membranes as the selective layer thickness decreases, causing anomalous gas transport properties and poor mixed-gas selectivities, which deviate from those of bulk membranes. To overcome this issue, a plasticization resistant (PR) layer is additionally coated onto the TFC membranes. Advanced thin-film characterization techniques, including quartz crystal microbalance (QCM) and nanomechanical analyses, demonstrate effective suppression of intensified plasticization in glassy polymer thin films by introducing a PR layer. Ultimately, the PR layer-coated TFC membranes exhibited excellent mixed-gas C3H6/C3H8 separation performances close to industrial requirements, which can be further extended to prepare large-area TFC membranes by roll-to-roll processes.
• #### Noncatalytic Oxidative Coupling of Methane (OCM): Gas-Phase Reactions in a Jet Stirred Reactor (JSR)

(ACS Omega, American Chemical Society (ACS), 2021-11-30) [Article]
Oxidative coupling of methane (OCM) is a promising technique for converting methane to higher hydrocarbons in a single reactor. Catalytic OCM is known to proceed via both gas-phase and surface chemical reactions. It is essential to first implement an accurate gas-phase model and then to further develop comprehensive homogeneous–heterogeneous OCM reaction networks. In this work, OCM gas-phase kinetics using a jet-stirred reactor are studied in the absence of a catalyst and simulated using a 0-D reactor model. Experiments were conducted in OCM-relevant operating conditions under various temperatures, residence times, and inlet CH4/O2 ratios. Simulations of different gas-phase models related to methane oxidation were implemented and compared against the experimental data. Quantities of interest (QoI) and rate of production analyses on hydrocarbon products were also performed to evaluate the models. The gas-phase models taken from catalytic reaction networks could not adequately describe the experimental gas-phase performances. NUIGMech1.1 was selected as the most comprehensive model to describe the OCM gas-phase kinetics; it is recommended for further use as the gas-phase model for constructing homogeneous–heterogeneous reaction networks.
• #### Oriented Two-Dimensional Covalent Organic Framework Membranes with High Ion Flux and Smart Gating Nanofluidic Transport.

(Angewandte Chemie, Wiley, 2021-11-24) [Article]
Nanofluidic ion transport holds high promise in bio-sensing and energy conversion applications. However, smart nanofluidic devices with high ion flux and modulable ion transport capabilities remain to be realised. Herein, we demonstrate smart nanofluidic devices based on oriented two-dimensional covalent organic framework (2D COF) membranes with vertically aligned nanochannel arrays that achieved a 2-3 orders of magnitude higher ion flux compared with that of conventional single-channel nanofluidic devices. The surface-charge-governed ion conductance is dominant for electrolyte concentration up to 0.01 M. Moreover, owing to the customisable pH-responsivity of imine and phenol hydroxyl groups, the COF-DT membranes attained an actively modulable ion transport with a high pH-gating on/off ratio of ~100. The customisable structure and rich chemistry of COF materials will offer a promising platform for manufacturing nanofluidic devices with modifiable ion/molecular transport features.
• #### Carbon dioxide/methane mixed-gas adsorption, permeation and diffusion in a carbon molecular sieve film: Experimental observation and modeling

(Journal of Membrane Science, Elsevier BV, 2021-11-20) [Article]
The CO2–CH4 pure- and mixed-gas transport properties (at 35 °C) of a carbon molecular sieve (CMS) film obtained by pyrolysis of a 6FDA-mPDA polyimide precursor at 900 °C are reported. The competitive mixed-gas adsorption of CO2 and CH4 was predicted by the Ideal Adsorbed Solution Theory (IAST) model. The CO2/CH4 mixed-gas solubility selectivity of the CMS film was lower than that of relevant glassy polymer films of various nature and increased with pressure. Mixed-gas adsorption data were coupled with gas permeation tests on the same film sample batch used for barometric adsorption measurements to derive concentration-averaged effective diffusion coefficients. Because of its large fraction of ultramicroporous bottlenecks, the diffusion coefficients of the CMS were of the same order of magnitude as those of glassy polymer films of low free volume (e.g., 6FDA-mPDA and CTA). In the range of pressures explored, the pure-gas and multicomponent CO2 diffusion coefficients overlapped; most importantly, the methane diffusion coefficient was enhanced by the presence of CO2. This result suggests that carbon dioxide dilated the sieving domains of the CMS matrix under mixed-gas environment containing highly sorbing gases such as CO2. Consequently, the CMS film lost some of its size-sieving properties as indicated by a drop in mixed-gas CO2/CH4 permselectivity relative to the values obtained under pure-gas conditions.
• #### High-Temperature Pyrolysis and Combustion of C5–C19 Fatty Acid Methyl Esters (FAMEs): A Lumped Kinetic Modeling Study

(Energy & Fuels, American Chemical Society (ACS), 2021-11-19) [Article]
In the effort to mitigate the depletion of fossil fuels and climate change, biodiesels are considered to be one of the most suitable substitutes for petro-diesel in compression ignition engine applications. As a follow up to prior modeling studies for gasoline and jet surrogate fuel components (Zhang, X.; Mani Sarathy, S. Fuel, 2021, 286, 119361), this work proposes a lumped kinetic model for both saturated and unsaturated C5–C19 fatty acid methyl esters (FAMEs) based on the same methodology. The present lumped model includes 52 FAME fuel components, covering a wide range of biodiesel surrogate fuel components, as well as components typically found in biodiesels. This methodology decouples the combustion of FAME fuels into two stages: the pyrolysis of fuel molecules and the oxidation of pyrolysis intermediates. Lumped reaction steps are used to describe the (oxidative) pyrolysis of each fuel molecule, while a detailed model (Aramcomech 2.0) is adopted as the base mechanism to describe the subsequent conversion of these key intermediates. Rate rules adopted for all the FAME fuels are consistent. The present lumped model is validated against experimental data from 20 pure FAMEs and six diesel/biodiesel surrogates, including around 130 sets of validation data. In general, the present lumped model satisfactorily captures most of these validation targets. This lumped model performs comparably with the detailed models developed in the literature under combustion conditions. Combined with the lumped model for 50 hydrocarbon fuels developed in previous work by this group, the lumped kinetic model for FAME fuels developed here can be used to predict the pyrolysis and combustion chemistry of diesel/biodiesel surrogates in CFD simulations after necessary model reduction for the base model. Also, the stoichiometric parameters of the lumped reactions for various pure FAMEs can be used as the database for data science study in FGMech development for real biodiesels.
• #### Evaporation, break-up, and pyrolysis of multi-component Arabian Light crude oil droplets at various temperatures

(International Journal of Heat and Mass Transfer, Elsevier BV, 2021-11-18) [Article]
Crude oil sprays are often used in direct combustion applications and refinery catalytic cracking units. Droplet evaporation, break-up, and pyrolysis are important aspects prior to gas-phase chemical reactions. This paper reports an experimental suspended droplet study of Arabian Light (AL) crude oil to assess the effect of ambiance temperature on dynamic events. Experiments were conducted at three different temperatures of 620 K, 710 K, and 840 K, to examine different regimes (devolatilization, transition stage, and complete pyrolysis) for several repetitions. Break-up events involved during the evaporation were successfully identified and classified into break-up modes depending on their break-up intensity (). Additionally, the effect of the temperature on the break-up events was assessed, showing that the number of break-up events increases exponentially with temperature. Finally, the density distribution of each break-up mode, as well as their final probability distribution were assessed. Intermediate and high-intensity break-ups (2-mode and 3-mode) break-ups were favored at lower temperatures, as well as micro-explosion (4-mode), in comparison with pyrolysis regime. However, break-up frequency increased exponentially with temperature. Additionally, based on the individual break-up modes density distributions characteristic times were identified successfully for pyrolysis regime, were the gasification dynamics changed. The global droplet behavior was examined by following the time evolution of the normalized droplet diameter. Two successive stages were identified at all temperature conditions: the swelling and the regression stage. In the devolatilization and the transition regimes, evaporation was controlled purely by the diffusive processes, whereas in the pyrolysis stage, the pure diffusion stage was not observed. Instead, a second swelling was registered, where an amorphous carbonaceous structure was formed. This was attributed to the pyrolysis of the heavy hydrocarbons in the droplet.
• #### Toward Liquid Phase Processable Metal Organic Frameworks: Dream or Reality?

(Accounts of Materials Research, American Chemical Society (ACS), 2021-11-11) [Article]