Catalytic dehydration of lactic acid and its esters is a promising approach to renewably produce acrylic acid and its esters. Molecular level understanding of the dehydration reaction mechanism on NaY has been achieved via a combination of reactivity and in-situ transmission Fourier Transform infrared (FTIR) spectroscopic investigations. Brønsted acid sites generated insitu with the assistance of water have been identified as the primary active sites for the dehydration pathway. The key branching point between the desired dehydration and undesired decarbonylation pathways is the dissociation of methyl lactate on NaY to form adsorbed sodium lactate and methyl groups. Brønsted and Lewis acid sites mainly catalyze the dehydration of adsorbed sodium lactate, whereas the decarbonylation pathway to acetaldehyde dominates when methyl lactate is not dissociated. Similar mechanistic steps are likely followed in the catalytic dehydration of lactic acid to acrylic acid. The mechanistic understanding gained will enable rational design of catalysts for selective dehydration of methyl lactate.

Catalytic dehydration of biomass-derived methyl lactate to produce acrylic acid and its esters promises a renewable route to produce a major commodity chemical. Alkali metal cation exchanged zeolites are capable of catalyzing this reaction, however, selectivity control toward the dehydration pathway remains a challenge. Through combined kinetic and transmission spectroscopic investigations, we demonstrate that introducing pyridine, a base, to the reaction feed increases selectivity to acrylates while inhibiting the formation of side products (i.e. acetaldehyde and coking). The ratio of the turnover frequencies for the desired dehydration and undesired decarbonylation pathways (TOF DH /TOF AD ) increases by a factor of ~20 when pyridine is included in the feed (pyridine/methyl lactate = 1/10), as compared to the case where pyridine is absent. Transmission FTIR investigations show that the reduced decarbonylation activity can be directly related to pyridine quenching Brønsted acid sites generated during the reaction, which are identified as the active sites for the decarbonylation pathway. Exposing NaY to pyridine prior to reaction does not impact the product distribution because Brønsted acid sites are produced by ion-exchange between NaY and reactants. In contrast, exposing NaY to pyridine containing feed for 1 h increases TOF DH /TOF AD after switching to a pyridine-free feed by a factor of ~4, as compared to the case where the catalyst is never exposed to pyridine.

Acrylic acid is a major commodity chemical currently produced almost entirely from petroleum-derived sources. The catalytic dehydration of methyl lactate is a promising renewable route to producing this vital chemical feedstock; however, enhancing the selectivity toward the dehydration pathway and catalyst stability remain challenging. We demonstrate a selectivity for dehydration products of ∼90% over a period of 30 h on NaY by introducing a small amount of pyridine in the reactant feed (pyridine/methyl lactate = 1:10). This increase in selectivity is attributed to the inhibition of side pathways, i.e., decarbonylation and coking, both of which are catalyzed by surface Brønsted acid sites generated in situ, rather than the acceleration of the dehydration pathway. Catalyst deactivation is shown to proceed through a drastically different mechanism in the absence and presence of pyridine in the feed via a combination of activity tests, thermogravimetric analysis, N 2 , and transmission FTIR spectroscopic investigations. Coke formation is the primary cause of catalyst deactivation in the pyridine-free feed, whereas when pyridine is used the accumulation of intact bulky and high boiling point acid/base complexes, e.g., pyridinium acrylate and pyridinium lactate, in the zeolite pores limits the access of reactant to the catalytic sites. Regeneration at 330−450 °C in inert atmosphere does not have any effect on the deactivated catalyst in the pyridine-free feed but partially restores the catalytic activity of the spent catalyst in pyridine-spiked feed. Porous catalysts with more open structures that facilitate the desorption of the bulky acid/base complexes are expected to be more resistant to deactivation.

Hydroxide exchange membrane fuel cells (HEMFCs) are an emerging low-cost alternative to conventional proton exchange membrane fuel cells. In addition to producing water at the anode, HEMFCs consume water at the cathode, leading to distinctive water transport behavior. We report that gas diffusion layer (GDL) wetproofing strictly lowers cell performance, but that the penalty is much higher when the anode side is wetproofed compared to the cathode side. We attribute this penalty primarily to mass transport losses from anode flooding, suggesting that cathode humidification may be more beneficial than anode humidification for this device. GDLs with little or no wetproofing perform best, yielding a competitive peak power density of 737 mW cm −2 .

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