Advances in Hydrocarbon and NOx Adsorbers

Dear Colleagues,

We are very excited to invite you to submit your manuscript for publication in Crystals, as we are preparing our Special Issue titled Advances in Hydrocarbon and NOx Adsorbers.

Modern automotive exhaust after-treatment systems consist of highly active NOx reduction and hydrocarbon (HC) oxidation catalysts that have proven efficient and meet current environmental regulations worldwide. However, as the regulations for criteria emissions become progressively more stringent, the automotive industry is facing the challenge of achieving near-zero NOx and HC emissions by 2025. The concepts of passive NOx adsorbers (PNAs) and hydrocarbon traps (HCTs) were originally introduced to address NOx and HC emissions during the cold start of internal-combustion engines, where the catalytic abatement of NOx and HC is less effective due to low exhaust temperatures.

An ideal PNA traps NOx at low temperatures and subsequently releases the NOx as the exhaust temperature increases and the downstream NOx reduction catalysts become highly effective. A similar strategy was proposed for low-temperature HC emissions with the help of HCTs. The past decade has witnessed significant progress in material synthesis and formulation development for PNAs and HCTs, and even more so in the last five years where materials with well-defined crystal structures were identified along with a large variety of unique chemistries. Recent advances in our understanding of NOx and HC storage and release mechanisms revealed some impactful crystal structure–property relations that are also beneficial to many other fields of material research.

To date, despite the significant research progress made in PNAs and HCTs, there are still many scientific questions to answer and industrial challenges to resolve. To give a few examples, it appears to be rather challenging to fully capture the NOx adsorption mechanism under realistic exhaust mixture and highly transient conditions; NOx storage sites and the precise crystal or defect structure needed for NOx adsorption on a PGM-free metal oxide passive NOx adsorber is often unclear; the NOx storage degradation problems of Pd-zeolite passive NOx adsorbers need further investigation and improvement; the dependency of HC storage behavior on the crystal structure of an HCT in the context of transient cold-start operation is not fully understood; the interplay between HCTs and the oxidation catalysts, especially upon HC release, seems to be very sensitive and have a convoluted impact on the HC speciation. Hence, we invite manuscript submissions on recent advances in hydrocarbon and NOx adsorber chemistry and engineering, which will address these challenges and other relevant questions.

Prof. William Epling
Dr. Yuntao (Kevin) Gu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• Crystal synthesis
• Metal oxides
• Zeolites
• NOx adsorption and reduction
• HC storage and oxidation
• Adsorption mechanism
• Storage sites
• Hydrothermal stability
• Degradation mechanism
• Transport properties