Search NASA⌕ Search

SEARCH · Search NASA

Results for “DEACTIVATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Nickel/gallium modified HZSM-5 for ethane aromatization: Influence of metal function on reactivity and stability

Bimetallic catalysts often outperform their monometallic counterparts due to the synergistic effect. Here we reported that the Ni/Ga co-functionalized HZSM-5 catalyst, specifically with Ni 1 /Ga 1 stoichiometric ratio, shows significantly improved selectivity (above 80 %) and stability than the Ni/HZSM-5 catalyst and higher activity (with identical selectivity) than the Ga/HZSM-5 catalyst in ethane aromatization. According to the transient experiment, the Ga and Ni 1 Ga 1 /HZSM-5 catalysts show an induction period of a few minutes. However, for Ni/HZSM-5 and Ni 1 Ga 1/3 /HZSM-5, the induction period increased to >10 min and >30 min, respectively, where up to 100 % of ethane was converted into methane and coke through cracking/hydrogenolysis. Furthermore, based on the generalized power-law equation model, a modified model for deactivation kinetic was proposed. Consequently, the influence of the metal function on the kinetic parameters was discussed. We anticipate the formation of Ni 3 Ga intermetallic alloy and its synergy with the exchanged Ga δ+ to be responsible for optimal BTX formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Benchmarking Cu/BEA and HBEA catalysts for high-octane gasoline synthesis

We distinguish rates at which carbon deposition occurs during initiation, rates at which catalytic centers are lost during deactivation, and paraffin-to-olefin ratio during propagation as benchmarks that distinguish 5 wt% Cu/H-BEA and H-BEA (Si/Al = 13.5) catalysts during dimethyl ether (DME) homologation in the presence of hydrogen. Studies that systematically vary initial DME contact time (210, 94, and 45 mol H+, initial s (mol C ) -1 ), DME pressure (4 and 22 kPa), and H 2 pressure (1, 24, and 48 kPa) reveal that Cu enables lower carbon deposition rates (on a per proton basis) in the induction period, increases the effluent paraffin-to-olefin ratio during propagation, and decreases the instantaneous site-loss yields by a factor of ~ 1.5-2x (moles of active sites lost per mole of DME) during termination sequences thus affecting the degree of product saturation and catalyst stability during DME homologation. Furthermore, these results provide mechanistic insights revealing the critical role of Cu in facilitating DME homologation to high value, high-octane gasoline-range hydrocarbons with higher cumulative turnovers than proton form H-BEA.

09 BIOMASS FUELS↗
DOE OSTI2022

Accelerating Catalyst Development for Biofuel Production through Multiscale Catalytic Fast Pyrolysis of Biomass over Mo2C

Advanced catalytic materials play an enabling role in producing renewable fuels and chemicals from biomass, thereby helping meet the global climate-change goals set forth by the Intergovernmental Panel on Climate Change. Herein, we present a multiscale approach to accelerate the catalyst-process development cycle for catalytic fast pyrolysis (CFP) of biomass over Mo2C. Mo2C has been shown to possess co-localized acidic and metallic sites and exhibit high activity for deoxygenation of biomass pyrolysis model compounds. However, critical knowledge gaps remain regarding the effectiveness of this catalyst for CFP of whole biomass. We address these knowledge gaps and demonstrate that Mo2C is effective at deoxygenating biomass-pyrolysis products in the presence of H2 but that it undergoes rapid selective and non-selective deactivation. The knowledge gaps addressed from this integrated study, targeting appropriate experiments across scales and feed types, enabled identification of critical modifications for advancing the CFP catalyst-process development cycle.

biofuels↗
DOE OSTI2018

Nonadiabatic dynamics simulations of photoexcited urocanic acid

Urocanic acid (UA) is a UV filter found in human skin, which has been linked to photoimmunosuppression and the formation of skin cancer. Its UV-light-induced photoisomerization and radiationless deactivation mechanisms have been addressed previously by static calculations. In this paper, we present nonadiabatic trajectory-surface-hopping dynamics simulations of photoexcited UA using the semiempirical OM2/MRCI methodology and an adaptive-timestep algorithm. We have simulated almost 6000 trajectories, each for a simulation time of 1.6 ps, covering the entire conformational space of the E and Z isomers of both possible tautomers of the isolated neutral form of UA (overall 32 conformers). Here, the initial conditions for the excited-state dynamics were obtained from 1 ns ground-state dynamics simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Catalytic fast pyrolysis with metal-modified ZSM-5 catalysts in inert and hydrogen atmospheres

The objective of this work was to determine the impact of hydrogen-activating metals on catalytic fast pyrolysis over ZSM-5 with and without hydrogen addition. Ga-, Ni-, Cu-, Co-, and Pt-modified ZSM-5 catalysts with metal-to-aluminum molar ratios of 2 were prepared by incipient wetness method. The catalysts were evaluated for hydrocarbon and oxygenate yields and for deactivation by analytical pyrolysis (Py-GC-MS), and post-reaction catalysts for characterization were prepared in a larger fixed-bed reactor. In inert atmosphere, there was a linear correlation between both the hydrocarbon yield and coke formation and density of strong acid sites, and the main impact of the metals was occlusion of active sites in ZSM-5, leading to proportional reductions in hydrocarbon and coke yields. With the addition of hydrogen, several metals (Pt, Ni, Cu, Co) activated hydrogen and further reduced coke formation, leading to improvements in the ratio of hydrocarbons to coke. No metal-modified catalyst out-performed fresh unmodified ZSM-5 in terms of hydrocarbon yield; however, Ni/ZSM-5 and Cu/ZSM-5 in hydrogen produced comparable hydrocarbon yields to ZSM-5 while reducing coke formation.

09 BIOMASS FUELS↗
DOE OSTI2019

Enhanced Catalyst Durability for Bio-Based Adipic Acid Production by Atomic Layer Deposition

Harsh reaction environments challenge the lifetime productivity of conventional catalysts and impede emerging biobased chemical processes. Condensed-phase processing of muconic acid, a biobased platform chemical, leads to problematic levels of catalyst leaching and fouling. Atomic layer deposition (ALD) can improve catalyst durability using protective metal oxide coatings; however, a targeted coating strategy and cost models thereof are needed for application-specific deactivation challenges that can surmount these challenges while accounting for process implications. Herein, we utilize thin (<5 wt% Al) Al2O3 ALD coatings to increase the lifetime productivity of Pd/TiO2 during muconic acid hydrogenation to adipic acid. The ALD coating decreases Pd leaching by >3x and markedly improves the thermal stability of Pd and TiO2. Economic analysis for an adipic acid biorefinery supports that increased material costs and reduced catalyst productivity can be justified through lifetime extension. Broadly, this work lays the foundation for reducing the cost of biobased chemical processes through catalyst stability.

Settle, Amy↗
DOE OSTI2016

Effects of the β1 auxiliary subunit on modification of Rat Na{sub v}1.6 sodium channels expressed in HEK293 cells by the pyrethroid insecticides tefluthrin and deltamethrin

We expressed rat Na{sub v}1.6 sodium channels with or without the rat β1 subunit in human embryonic kidney (HEK293) cells and evaluated the effects of the pyrethroid insecticides tefluthrin and deltamethrin on whole-cell sodium currents. In assays with the Na{sub v}1.6 α subunit alone, both pyrethroids prolonged channel inactivation and deactivation and shifted the voltage dependence of channel activation and steady-state inactivation toward hyperpolarization. Maximal shifts in activation were ~ 18 mV for tefluthrin and ~ 24 mV for deltamethrin. These compounds also caused hyperpolarizing shifts of ~ 10–14 mV in the voltage dependence of steady-state inactivation and increased in the fraction of sodium current that was resistant to inactivation. The effects of pyrethroids on the voltage-dependent gating greatly increased the size of sodium window currents compared to unmodified channels; modified channels exhibited increased probability of spontaneous opening at membrane potentials more negative than the normal threshold for channel activation and incomplete channel inactivation. Coexpression of Na{sub v}1.6 with the β1 subunit had no effect on the kinetic behavior of pyrethroid-modified channels but had divergent effects on the voltage-dependent gating of tefluthrin- or deltamethrin-modified channels, increasing the size of tefluthrin-induced window currents but decreasing the size of corresponding deltamethrin-induced currents. Unexpectedly, the β1 subunit did not confer sensitivity to use-dependent channel modification by either tefluthrin or deltamethrin. We conclude from these results that functional reconstitution of channels in vitro requires careful attention to the subunit composition of channel complexes to ensure that channels in vitro are faithful functional and pharmacological models of channels in neurons. - Highlights: • We expressed Na{sub v}1.6 sodium channels with or without β1 subunits in HEK293 cells. • Tefluthrin and deltamethrin shifted channel gating to hyperpolarized potentials. • The β1 subunit had opposite effects on the actions of tefluthrin and deltamethrin. • Auxiliary subunits are required for full reconstitution of channel function. • Channels in HEK293 cells exhibit properties similar to channels in neurons.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Pt-Assisted Carbon Remediation of Mo2C Materials for CO Disproportionation

Using the CO disproportionation (Boudouard) reaction as a probe reaction, an in-depth analysis of temperature-programmed pulse response data shows that the addition of Pt to Mo2C mitigates deactivation of Mo active sites by acting as a carbon collector. CO2 production on Mo2C and Pt/Mo2C materials is dependent on both the activation energy and the CO surface concentration. Detailed plane-wave density functional theory calculations of the CO adsorption and disproportion reactions on Mo2C-supported Pt nanoparticles (NPs) are reported. The Mo2C was modeled by the ß-Mo2C (100) surface, and the Pt/Mo2C interface was modeled by the addition of 12 Pt atoms to the Mo2C (100) surface (12Pt@Mo2C). The potential energy surfaces of the Boudouard reaction were calculated on pure Mo2C, 12Pt@Mo2C, and Pt (111) surfaces. CO dissociation readily occurs on the Mo2C (100) surface, but not on the Pt (111) surface, with the former being exothermic and the latter being endothermic. At the Pt/Mo2C interface, CO dissociation is still exothermic, but with a larger energy barrier. The Boudouard reaction takes place on the Mo2C region, where CO2 is formed from a surface O atom dissociated from one CO molecule in reaction with another CO molecule, leaving one C atom on the surface. C adsorption is preferential on the Pt site in comparison to the Mo site. The supported Pt domains can collect the remaining C atoms, facilitating further CO2 formation on the active Mo sites. A Bader charge analysis shows that the surface metal-carbon bond is a mixture of covalent and ionic bonds, whereas the surface metal-oxygen bond is ionic. Electron localization function (ELF) and partial charge density calculations agree well with the Bader charge analysis. These computational results are consistent with experimental observations of the interaction of CO with Mo2C nanotube supported Pt domains in the transient regime under far from equilibrium conditions. The Boudouard reaction is an important side reaction, and the unexpected role found for Pt as a carbon collector, with Mo serving as a disproportionation site, provides a unique vantage point for understanding carbon and coke formation on catalytic materials.

Pt-assisted carbon remediation, Pt/Mo2C interface,↗
DOE OSTI2022

Monolayer Molecular Functionalization Enabled by Acid–Base Interaction for High-Performance Photochemical CO 2 Reduction

We report the development of a hybrid catalyst consisting of carbon nitride (CN x ) and cobalt phthalocyanine tetracarboxylic acid (CoPc-COOH), which converts CO 2 to CO with high reaction rate (1067 μmol/g·h) and high selectivity (over 98%), under simulated solar irradiation. The carboxylic acid substituents on the phthalocyanine ligands play a critical role as they bind to the amine groups of CN x to enable nearly ideal monolayer coverage of the molecular co-catalyst on the semiconductor surface and promote catalytic activity from the molecular complex. Specifically, the CN x /CoPc-COOH hybrid material achieves a reaction rate 16 times higher than a CN x material containing unsubstituted CoPc molecules. We further show that activation and deactivation of the CN x /CoPc-COOH composite, which are associated with the reduction and decomposition of CoPc-COOH, respectively, both proceed at a nearly constant rate regardless of the CO 2 reduction reaction rate. Here, the decoupling of charge carrier injection and CO 2 reduction catalysis has important mechanistic implications for future performance optimization and materials design of photocatalysts for CO 2 reduction.

14 SOLAR ENERGY↗
DOE OSTI2024

Butene-Rich Alkene Formation from 2,3-Butanediol through Dioxolane Intermediates

The cost-effective production of sustainable aviation fuels (SAF) remains a major challenge within the energy sector. One approach to address this is the fermentation of biomass feedstocks into oxygenates followed by catalytic conversion to alkenes or other oligomerization precursors. 2,3-Butanediol (BDO) is a promising fermentation product due to its four-carbon nature, its decreased microorganism toxicity and associated higher maximum fermentation titers relative to other alcohols and oxygenates, and its capacity to be readily converted into butene isomers and longer chain alkenes. BDO conversion is currently constrained by separation challenges for BDO isolation due to its high boiling point and hydrophilicity. Here, this work expands upon previous BDO reactive separation via dioxolane formation over a solid acid catalyst by investigating the conversion of dioxolanes into alkene mixtures. Dioxolanes were formed from a range of aldehydes and subsequently converted over a Cu/ZSM-5 catalyst (448–523 K) via an ether cleavage, hydrogenation, and dehydration reaction network to form alkene-rich product mixtures (96% C 3+ alkene yield, 523 K). This selectivity is greater than that of direct BDO conversion to alkenes over an identical catalyst (89%, 523 K). C 3+ alkene selectivity is maximized between 498 and 523 K at complete dioxolane conversion without significant alkene hydrogenation to alkanes. The alkene product distributions can be tailored via both aldehyde selection during dioxolane formation and the dioxolane conversion reaction temperature. Alkene mixtures from dioxolane conversion predominantly reflect the carbon chain length and stereochemistry of BDO and the initial aldehyde at or below 498 K, yet higher reaction temperatures yield alkene mixtures of similar carbon chain distributions, regardless of initial aldehyde selection. Deactivation of the Cu/ZSM-5 catalyst is observed for multiple steps of the overall reaction network but can be minimized by facilitating the complete dioxolane-to-alkene reaction network at temperatures of at least 498 K.

2,3-butanediol↗
DOE OSTI2019

Highly Selective Heterogeneous Ethylene Dimerization with a Scalable and Chemically Robust MOF Catalyst

Metal–organic frameworks (MOFs) hold great promise as structurally tunable catalysts capable of high selectivity in the solid state, yet their comparatively high cost and often limited stability remain significant concerns for their commercialization as heterogeneous catalysts. In this paper, we report detailed X-ray absorption spectroscopy studies of Co- and Ni-MFU-4$l$, a class of highly selective MOF catalysts for olefin upgrading, and reveal mechanisms that lead to their deactivation. We further show that Ni-CFA-1, a more scalable and economical alternative to Ni-MFU-4l, reproduces both the local coordination structure and the high selectivity of the latter in ethylene dimerization catalysis. Under optimal conditions, Ni-CFA-1 activated by MMAO-12 achieves a turnover frequency of 37100 per hour and a selectivity of 87.1% for 1-butene, a combination of activity, selectivity, and affordability that is unmatched among heterogeneous ethylene dimerization catalysts. Ni-CFA-1 retains its high activity for at least 12 h in a one-liter semibatch reactor, offering a strategy toward robust and scalable MOFs for industrial catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Coupled slow and fast surface dynamics in an electrocatalytic oscillator: Model and simulations

The co-existence of disparate time scales is pervasive in many systems. In particular for surface reactions, it has been shown that the long-term evolution of the core oscillator is decisively influenced by slow surface changes, such as progressing deactivation. Here we present an in-depth numerical investigation of the coupled slow and fast surface dynamics in an electrocatalytic oscillator. The model consists of four nonlinear coupled ordinary differential equations, investigated over a wide parameter range. Besides the conventional bifurcation analysis, the system was studied by means of high-resolution period and Lyapunov diagrams. It was observed that the bifurcation diagram changes considerably as the irreversible surface poisoning evolves, and the oscillatory region shrinks. The qualitative dynamics changes accordingly and the chaotic oscillations are dramatically suppressed. Nevertheless, periodic cascades are preserved in a confined region of the resistance vs. voltage diagram. Numerical results are compared to experiments published earlier and the latter reinterpreted. Finally, the comprehensive description of the time-evolution in the period and Lyapunov diagrams suggests further experimental studies correlating the evolution of the system's dynamics with changes of the catalyst structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Cascade energy transfer versus charge separation in ladder-type oligo(p-phenylene)/ZnO hybrid structures for light-emitting applications

Usability of inorganic/organic semiconductor hybrid structures for light-emitting applications can be intrinsically limited by an unfavorable interfacial energy level alignment causing charge separation and nonradiative deactivation. Introducing cascaded energy transfer funneling away the excitation energy from the interface by transfer to a secondary acceptor molecule enables us to overcome this issue. We demonstrate a substantial recovery of the light output along with high inorganic-to-organic exciton conversion rates up to room temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Lattice distortion mechanism study of TiO{sub 2} nanoparticles during photocatalysis degradation and reactivation

In this paper, the photocatalytic process of TiO{sub 2} (P25) is directly characterized by using a positron annihilation lifetime spectroscopy (PALS), high-resolution transmission electron microscopy (HRTEM), Photoluminescence spectroscopy (PL) and UV Raman spectroscopy (Raman). The experimental results reveal that: 1) From PALS measurements, because τ{sub 1} and τ{sub 2} values and their intensity (I{sub 1} and I{sub 2}) assigned to the different size and amounts of defects, respectively, their variations indicate the formation of different types and amounts of defects during the absorption and degradation. 2) HRTEM observations show that the lattice images become partly blurring when the methylene blue is fully degradated, and clear again after exposed in the air for 30 days. According to the results, we propose a mechanism that the lattice distortion induces the defects as electron capture sites and provides energy for improving photocatalytic process. Meanwhile, the lattice distortion relaxation after exposing in the air for 30 days perfectly explains the gradual deactivation of TiO{sub 2}, because the smaller vacancy defects grow and agglomerate through the several photocatalytic processes. The instrumental PL and Raman are also used to analyze the samples and approved the results of PALS and HRTEM.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The geometrical change and intramolecular energy transfer upon S{sub 1}←S{sub 0} excitation in cyclopentanone

The ultrafast dynamics in vibrationally hot S{sub 1} electronic excited state in cyclopentanone molecule was discovered with time resolved spectroscopy. Investigation of the geometry change upon the S{sub 1}←S{sub 0} excitation and D{sub 0}←S{sub 1} ionization has shown that the dihedral angle between the C=O bond and the plane given by the carbonyl and the α-carbons is 180° either in S{sub 0} or D{sub 0} state and is reduced to 145.8° by out-out-plane deformation of the oxygen in S{sub 1} state according to the theoretical calculation. The time domain experiments with femtosecond resolution have given rich insights into the energy transfer of the cyclopentanone molecule. The molecules are excited to the vibrationally hot S{sub 1} (n, π{sup ∗}) state following absorption of one 267-nm photon. It is found that the population of the S{sub 1} (n, π{sup ∗}) state undergoes ultrafast internal conversion to the highly vibrationally hot S{sub 0} state within 80 fs and nonradiative deactivation by intersystem crossing to triplet T{sub 1} (n, π{sup *}) state occurring in 3.14 ps. Several Rydberg states have worked as stepping stones during the ionization. The available energy was distributed in the symmetric methylene group wagging and the symmetric skeletal ring breathing modes in D{sub 0} state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Erratum to: “The Fluorescence and Electronic Structure of Phenyl-Substituted Tetraazachlorin Molecules” [Optics and Spectroscopy 117, 722 (2014)]

should read “porphyrazine” instead of “porphyrazin”;should read “intersystem crossing” instead of “intercombinational conversion”;should read “mirror-symmetrical” instead of “reflection-symmetric”;should read “fluorescence enhancement” instead of “fluorescence buildup.”Page 722, Abstract, lines 9–10 from the top, the sentence should read:This characteristic increases upon tetrapyrrole phenylation.Page 727, left column, lines 17–18 from the top, the sentence should read:The vibronic transition parts of the emission spectrum are diffuse, (…)Page 727, left column, lines 29–30 from the top, the sentence should read:Note that the Stokes shift in these cases is relatively large.Page 729, left column, lines 8–10 from the bottom, the sentence should read:For H{sub 2}Ph{sub 8}TAC{sup mp} and H{sub 2}Ph{sub 6}TAC{sup tm}, the enhancement of fluorescence is weaker than in the former case: on cooling, τ{sub F} is increased by a factor of 4–5 in MTHF and by a factor of only 2.6–3 in toluene.Page 729, right column, lines 9–10 from the footnote, the sentence should read:It is seen from Table 1 that our results agree reasonably well with previously reported data.Page 730, left column, lines 16–19 from the top, the sentence should read:The lifetime for the outgassed H{sub 2}TAP solution intoluene (τ{sub T}{sup 0}) was measured by A.S. Stasheuski as phosphorescence decay at λ{sub reg} = 1070 nm using the setup described in [29].Page 730, left column, lines 20–23 from the top, the sentence should read:The τ{sub T} value derived from the kinetics of the rise of singlet oxygen luminescence [26] for the nonoutgassed solution at λ{sub reg} = 1272 nm is 162 ns;Page 730, right column, lines 25–27 from the top, the sentence should read:Therefore, for H{sub 2}TAP (λ{sub F}{sup 00}≈ 620 nm), the internal conversion probability should not be high.Page 731, left column, the heading of Table 2 should read:Bond lengths in the porphine macrocycle (Å).Page 731, left column, lines 3–6 from the top, the sentence should read:For elucidating the mechanism of the deactivation of the S{sub 1} state, it was of essential interest to see whether the enhancement of H{sub 2}TAP fluorescence would be observed at 77 K.Page 733, left column, lines 2–3 from the top, the sentence should read:The corresponding difference for the H{sub 2}P–H{sub 2}C pair is 0.013 Å.Page 733, left column, lines 14–16 from the top, the sentence should read:The macrocycle undergoes additional contraction, and the symmetry of its conjugated system is very close to D{sub 2h}.Page 733, right column, line 21 from the top should read:Replacement of the methine bridges (…)Page 734, left column, lines 8–11 from the figure caption, the sentence should read:This is the main reason of the large bathochromic shift of the Soret band of H{sub 2}Ph{sub 8}TAP and MgPh{sub 8}TAP [16] relative to H{sub 2}TAP and MgTAP, respectively.Page 734, left column, lines 1–4 from the bottom, the sentence should read:The complete INDO/Sm calculation yields the corresponding quantitative characteristics, which are in good agreement with experimental data (see below).Page 740, left column, reference no. 25 should read:25. V. A. Galievsky, A. S. Stasheuski, V. V. Kiselyov, A. I. Shabusov, M. V. Belkov, and B. M. Dzhagarov, Instrum. Exp. Tech. 53, 568 (2010).25. V. A. Galievsky, A. S. Stasheuski, V. V. Kiselyov, A. I. Shabusov, M. V. Belkov, and B. M. Dzhagarov, Instrum. Exp. Tech. 53, 568 (2010).30. V. L. Ermolaev and E. B. Sveshnikova, Acta Phys. Pol. 34, 771 (1968).

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Recent Progress to Understand and Improve Zeolite Stability in the Aqueous Medium

The work reviewed here attempts to summarize the growing literature on zeolite stability in hot liquid water. This required to first establish the nature, structure and interactions of the active sites in Brønsted and Lewis acidic microporous materials in the presence of liquid water. This understanding was then transferred to zeolite stability and catalyst deactivation. While early results correctly established Si–O–Si hydrolysis as the dominant pathway compared to the Si–O–Al hydrolysis observed in steaming, it also focused extensively on the positive role of framework and extra-framework Al in stabilizing zeolites. However, stability was instead found to more directly correlate with the number of internal structural defects and intraporous water concentration. Stabilization protocols for Brønsted acidic zeolites are described in detail. In the case of Lewis acidic zeolites, their inherent hydrophobic behavior (Si/M >100) makes them more resistant towards water, however, issues such as reversible carbonaceous species formation as well as irreversible metal leaching and fouling remain. Finally, we summarize the most important factors in designing robust and efficient zeolite catalysts made to withstand hot liquid water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗