MDPI - Publisher of Open Access Journals

11 pages, 3747 KiB

Open AccessEditor’s ChoiceArticle

Enhancing the Activity of Cu-MOR by Water for Oxidation of Methane to Methanol

by Xi’an Guan, Yehong Wang, Xiumei Liu, Hong Du, Xinwen Guo and Zongchao Zhang

Catalysts 2023, 13(7), 1066; https://doi.org/10.3390/catal13071066 - 3 Jul 2023

Cited by 3 | Viewed by 2053

As clean energy, methane has huge reserves and great development potential in the future. Copper zeolites are efficient in the oxidation of methane to methanol. Water has been confirmed as a source of oxygen to regenerate the copper-zeolite active sites to enable selective anaerobic oxidation of methane to methanol. In this work, we report that the methanol yield increased from 36 μmol/g (Cu-MOR₁) to 92 μmol/g (Cu-MOR₁-water) as a result of water enhancing the activity of copper ion-exchange mordenite catalyst. We show for the first time that water could convert inactive copper species into active copper species during catalyst activation. A combination of the XPS, FTIR, and NMR results indicates that water dissociates and then converts ZCu^IIZ into ZCu^II(OH) (where Z indicates framework O (O_fw) bonded to one isolated Al in a framework T-site, i.e., 1Al) and simultaneously produces a Brönsted acid site during catalyst activation. This finding can be used to tune the state of copper species and design highly active copper-zeolite catalysts for methane oxidation to methanol. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Clean Energy Production and Carbon Dioxide Utilization)

► Show Figures

Graphical abstract

11 pages, 1474 KiB

Open AccessFeature PaperArticle

The H₂O Effect on Cu Speciation in Cu-CHA-Catalysts for NH₃-SCR Probed by NH₃ Titration

by Roberta Villamaina, Federica Gramigni, Umberto Iacobone, Shaojun Liu, Isabella Nova, Enrico Tronconi, Maria Pia Ruggeri, Jillian Collier, Andrew P. E. York and David Thompsett

Catalysts 2021, 11(7), 759; https://doi.org/10.3390/catal11070759 - 23 Jun 2021

Cited by 13 | Viewed by 3098

Abstract

The present work is focused on the effect of water on NH₃ adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO₂/Al₂O₃) ratios and Cu loadings were studied under both dry and wet conditions. H₂O adversely affects NH₃ adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH₃ desorption at low temperature during TPD. Interestingly, the NH₃/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH₃) or 1–2 (no gaseous NH₃) in dry conditions, in line with the formation of different NH₃-solvated Cu species (e.g., [Cu^II(NH₃)₄]²⁺ and [Cu^II(OH)(NH₃)₃]⁺ with gaseous NH₃, [Z₂Cu^II(NH₃)₂]²⁺ and [ZCu^II(OH)(NH₃)]⁺ without gaseous NH₃). When H₂O was fed to the system, on the contrary, the NH₃/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H₂O and NH₃ for adsorption on Lewis sites and with the hydrolysis of a fraction of Z₂Cu^II species into ZCu^IIOH. Full article

(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)

► Show Figures

Figure 1

Search Results (2)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (2)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI