Abundance and Speciation of Surface Oxygen on Nanosized Platinum Catalysts and Effect on Catalytic Activity

Serra-Maia, Rui; Winkler, Christopher; Murayama, Mitsuhiro; Tranhuu, Kevin; Michel, F. Marc

doi:10.1021/acsaem.8b00474

Cited by 13 publications

(14 citation statements)

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“…These conditions reconcile results from previous studies that could not be explained thus far. For example, heterogeneous metallic platinum is a good catalyst for H 2 O 2 decomposition. , However, this catalyst has never been successfully employed for the oxidative methane upgrade because platinum-catalyzed H 2 O 2 decomposition does not proceed via a radical-based mechanism. , Likewise, radiation-induced ·OH generation has been used to oxidize methane, but methanol was not present in the products, because step 3.2 does not occur in the absence of AuPd − (Figure ). Similarly, Fenton catalysts decompose H 2 O 2 through a radical pathway and thus should catalyze the conversion of CH 4 to CH 3 OH.…”

Section: Resultsmentioning

confidence: 99%

Mechanism and Kinetics of Methane Oxidation to Methanol Catalyzed by AuPd Nanocatalysts at Low Temperature

et al. 2021

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The selective oxidation of methane to methanol at ambient conditions has the potential to enable the use of natural gas obtained in remote areas. We performed multivariate statistical analysis of 137 laboratory experiments to show that gold–palladium nanocatalysts unlock the reaction pathway that forms methanol, but the overall rate of methane oxidation does not correlate with the total number of active sites because the catalyst does not participate in the rate limiting step of the reaction. Using an H2O2 concentration below 2.5 × 10–5 mol/L reduces the H2O2 overuse up to 10,000 times and promotes a methanol selectivity greater than 0.8 without compromising the reaction productivity. These results have enormous practical importance for methane utilization because they explain the poor methane conversion rates obtained thus far and show the path to increase the methanol productivity and reduce the overuse of industrially expensive H2O2.

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Section: Resultsmentioning

confidence: 99%

Mechanism and Kinetics of Methane Oxidation to Methanol Catalyzed by AuPd Nanocatalysts at Low Temperature

et al. 2021

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“…The first order effect of H 2 O 2 concentration in the rate of H 2 O 2 decomposition by AuPd nanocatalysts observed here is consistent with previous reports. This indicates that in the rate limiting step of the reaction one H 2 O 2 molecule reacts with one active site at a time. ,, This is important because from reactions –, it is anticipated that to form methanol one molecule of methane and one molecule of OH* must react together. Because radical species are unstable, in steady state, the rate of OH* formation and decomposition are equal (eq ), and the rate of methanol formation is proportional to the concentration of methane and OH* in solution (eq ) …”

Section: Resultsmentioning

confidence: 99%

Decomposition of Hydrogen Peroxide Catalyzed by AuPd Nanocatalysts during Methane Oxidation to Methanol

et al. 2020

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Selective oxidation of methane into energy-dense liquid derivatives at low temperature and pressure is critical for enabling the use of vast natural gas reserves around the world. This has been recently achieved with AuPd nanocatalysts, but the process exhibits accelerated rates of deleterious H2O2 self-decomposition, which results in prohibitive industrial costs. We performed a multivariate analysis of 143 H2O2 decomposition rate measurements reported in the literature to quantify the effect of reaction conditions and catalyst properties in the decomposition of H2O2 at conditions used during methane upgrading. The results show that the reaction is first order in terms of H2O2 concentration and correlates with a larger particle size. The catalytic activity of colloidal AuPd is lower than that of supported AuPd. The effect of methane pressure is practically negligible, which is evidenced by an H2O2 decomposition rate only 42% smaller when the methane pressure is increased more than 6 log-units. Overall, the results indicate that methane oxidation occurs in a significant excess of H2O2, which contributes to its radical-based self-decomposition. Inhibiting the activity of AuPd nanocatalysts toward H2O2 self-decomposition is key to achieving high H2O2 efficiency use for the oxidation of methane to methanol. This can be done by decreasing the concentration of H2O2, using smaller AuPd nanocatalysts, increasing the Au/Pd ratio, using colloidal versus supported nanocatalysts, or increasing the pressure of methane in the reactor. The results of this study provide a path for targeted AuPd catalyst optimization for methane upgrading with improved H2O2 decomposition efficiency and high methane oxidation productivity.

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“…The elongation observed on Pt black crystallites occurs along random directions, and no particular crystallographic plane is preferentially exposed for either catalyst. When dispersed in aqueous solutions the crystallites of both catalyst samples are partly aggregated and the extent of aggregation is similar for both [ID am-2018-023446] …”

Section: Resultsmentioning

confidence: 99%

“…This article reports the rates of H 2 O 2 decomposition as a function of H 2 O 2 concentration, pH, and temperature by two common Pt nanocatalysts, known as Pt black and Pt nanopowder. Our characterization of these samples, which have different average crystal size and shape characteristics, revealed new information regarding the abundance and speciation of surface oxygen [ID am-2018-023446] . The results from this study showed that oxygen at the surfaces is primarily chemisorbed with platinum and that its abundance increases with increasing particle size.…”

Section: Introductionmentioning

confidence: 88%

Mechanism and Kinetics of Hydrogen Peroxide Decomposition on Platinum Nanocatalysts

Serra-Maia

Bellier

Chastka

et al. 2018

ACS Appl. Mater. Interfaces

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The decomposition of HO to HO and O catalyzed by platinum nanocatalysts controls the energy yield of several energy conversion technologies, such as hydrogen fuel cells. However, the reaction mechanism and rate-limiting step of this reaction have been unsolved for more than 100 years. We determined both the reaction mechanism and rate-limiting step by studying the effect of different reaction conditions, nanoparticle size, and surface composition on the rates of HO decomposition by three platinum nanocatalysts with average particle sizes of 3, 11, and 22 nm. Rate models indicate that the reaction pathway of HO decomposition is similar for all three nanocatalysts. Larger particle size correlates with lower activation energy and enhanced catalytic activity, explained by a smaller work function for larger platinum particles, which favors chemisorption of oxygen onto platinum to form Pt(O). Our experiments also showed that incorporation of oxygen at the nanocatalyst surface results in a faster reaction rate because the rate-limiting step is skipped in the first cycle of reaction. Taken together, these results indicate that the reaction proceeds in two cyclic steps and that step 1 is the rate-limiting step. Step 1: Pt + H O → H O + Pt( O). Step 2: Pt( O) + H O → Pt + O + H O. Overall: 2 H O → O + 2 H O. Establishing relationships between the properties of commercial nanocatalysts and their catalytic activity, as we have done here for platinum in the decomposition of HO, opens the possibility of improving the performance of nanocatalysts used in applications. This study also demonstrates the advantage of combining detailed characterization and systematic reactivity experiments to understand property-behavior relationships.

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Abundance and Speciation of Surface Oxygen on Nanosized Platinum Catalysts and Effect on Catalytic Activity

Cited by 13 publications

References 125 publications

Mechanism and Kinetics of Methane Oxidation to Methanol Catalyzed by AuPd Nanocatalysts at Low Temperature

Mechanism and Kinetics of Methane Oxidation to Methanol Catalyzed by AuPd Nanocatalysts at Low Temperature

Decomposition of Hydrogen Peroxide Catalyzed by AuPd Nanocatalysts during Methane Oxidation to Methanol

Mechanism and Kinetics of Hydrogen Peroxide Decomposition on Platinum Nanocatalysts

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