Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Controlling surface structure at the atomic scale is paramount to developing effective catalysts. For example, the edge sites of MoS(2) are highly catalytically active and are thus preferred at the catalyst surface over MoS(2) basal planes, which are inert. However, thermodynamics favours the presence of the basal plane, limiting the number of active sites at the surface. Herein, we engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS(2) bicontinuous network with nanoscaled pores. The high surface curvature of this catalyst mesostructure exposes a large fraction of edge sites, which, along with its high surface area, leads to excellent activity for electrocatalytic hydrogen evolution. This work elucidates how morphological control of materials at the nanoscale can significantly impact the surface structure at the atomic scale, enabling new opportunities for enhancing surface properties for catalysis and other important technological applications.

Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis

Progress in catalysis is driven by society's needs. The development of new electrocatalysts to make renewable and clean fuels from abundant and easily accessible resources is among the most challenging and demanding tasks for today's scientists and engineers. The electrochemical splitting of water into hydrogen and oxygen has been known for over 200 years, but in the last decade and motivated by the perspective of solar hydrogen production, new catalysts made of earth-abundant materials have emerged. Here we present an overview of recent developments in the non-noble metal catalysts for electrochemical hydrogen evolution reaction (HER). Emphasis is given to the nanostructuring of industrially relevant hydrotreating catalysts as potential HER electrocatalysts. The new syntheses and nanostructuring approaches might pave the way for future development of highly efficient catalysts for energy conversion.

/pdf/nanostructured-hydrotreating-catalysts-for-electrochemical-38x9bd6n29.pdf

Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution

An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel

Science and technology of novel processes for deep desulfurization of oil refinery streams: a review☆ ☆

The production of clean diesel by hydrotreating and deep hydrodesulfurization (HDS) has attracted increased attention recently due to the introduction of new environmental legislation regarding fuel specifications. In order to meet the specifications there is a need to modify and improve existing reactors and processes and to introduce more active and selective catalysts. The removal of sterically hindered sulfur-containing molecules is observed to be a key issue for deep HDS. Also the choice of operation conditions and reactor internals play an important role for deep HDS. The present article will focus on key hydrotreating options available to obtain ultra low sulfur diesel levels and some of the theoretical and experimental structure–activity relationships which may aid catalyst developments.

Catalyst and process technologies for ultra low sulfur diesel

To produce diesel fuel from renewable organic material such as vegetable oils, it has for a number of years been known that triglycerides can be hydrogenated into linear alkanes in a refinery hydrotreating unit over conventional sulfided hydrodesulfurization catalysts. A number of new reactions occur in the hydrotreater, when a biological component is introduced, and experiments were conducted to obtain a more detailed understanding of these mechanisms. The reaction pathways were studied both in model compound tests and in real feed tests with mixtures of straight-run gas oil and rapeseed oil. In both sets of experiments, the hydrogenation of the oxygen containing compounds was observed to proceed either via a hydrodeoxygenation (HDO) route or via a decarboxylation route. The detailed pathway of the HDO route was further illuminated by studying the hydroprocessing of methyl laurate into n-dodecane. The observed reaction intermediates did not support a simple stepwise hydrogenation of the aldehyde formed after hydrogenation of the connecting oxygen in the ester. Instead, it is proposed that the aldehyde formed is enolized before further hydrogenation. The existence of an enol intermediate was further corroborated by the observation that a ketone lacking α-hydrogen (that cannot be directly enolized) had a much lower reactivity than a corresponding ketone with α-hydrogen. In real feed tests, the complete conversion of rapeseed oil into linear alkanes at mild hydrotreating conditions was demonstrated. From the gas and liquid yields, the relative rates of HDO and decarboxylation were calculated in good agreement with the observed distribution of the n-C17/n-C18 and n-C21/n-C22 formed. The hydrogen consumption associated with each route is deduced, and it was shown that hydrogen consumed in the water-gas-shift and methanization reactions may add significant hydrogen consumption to the decarboxylation route. The products formed exhibited high cetane values and low densities. The challenges of introducing triglycerides in conventional hydrotreating units are discussed. It is concluded that hydrotreating offers a robust and flexible process for converting a wide variety of alternative feedstocks into a green diesel fuel that is directly compatible with existing fuel infrastructure and engine technology.

Kim G. Knudsen

Papers

Catalyst and process technologies for ultra low sulfur diesel

Hydroprocessing of Bio-Oils and Oxygenates to Hydrocarbons. Understanding the Reaction Routes

The role of reaction pathways and support interactions in the development of high activity hydrotreating catalysts

Comparative atomic-scale analysis of promotional effects by late 3d-transition metals in MoS2 hydrotreating catalysts

Atomic-scale insight into adsorption of sterically hindered dibenzothiophenes on MoS2 and Co–Mo–S hydrotreating catalysts