Proliferating
energy consumption, particularly of fossil fuels,
has led to an increasing generation of pollutants; many of these harmful
products have been of serious environmental concern. While energy
demand will continue to grow due to massive urbanization and industrialization,
the ability to remove such pollutants has not yet been achieved. Therefore,
policies are always being reviewed to accommodate the existing reality
of minimizing the amount of pollutants released to the environment
on a daily basis. Sulfur dioxide, a major environmental pollutant,
gets to the environment through the combustion of sulfur-containing
fuel in the engine of automobiles. Over the years, regulatory bodies
such as the European Emission Standard have set limits to the amount
of sulfur in transportation fuel to safeguard the environment. Lately,
the limit for clean fuel specification with respect to sulfur content
is set to nearly zero ppm. This policy came at a time when crude oil
experienced a large decline in price, in addition to increased sulfur
content and daily fluctuations of crude density. Compliance with this tight regulation will mean that refineries
are expected to either modify their hydrotreating unit, which is capital
intensive, or adopt robust catalysts, through research, that can work
in tandem with the existing conventional hydrotreating catalysts to
reduce the sulfur level to the required limit. This urgent demand
has once more drawn the attention of the scientific community. Since
there has been a great stock of research outcomes with respect to
catalysts for hydrodesulfurization application in recent times, our
aim is to collect and review those recent articles on hydrodesulfurization
catalyst design and development. The tutorial review is therefore
intended to cover a basic hydrodesulfurization overview, followed
by detailed discussions on the recent development in the choice of
active phases, their supports, and synthesis strategies. The work
is expected to guide researchers, especially beginners that are interested
in refinery hydrotreatment, on the recent development in hydrodesulfurization
catalyst design and development.
CeOx–Si–CoMo catalysts for efficient hydrodesulfurization (HDS) activity of dibenzothiophene: role of ceria in catalyst activity and product selectivity.
The direct conversion of crude oil to light olefins is considered one the cheapest and most reliable sources of petrochemical primary feedstocks. Unlike in the past when refineries operated to produce mainly transportation fuels, such as gasoline and diesel, many refineries worldwide are considering tandem production of both fuels and chemicals (particularly, light olefins). To achieve this, refining technology, process optimization, and catalyst formulations may have to be reconfigured. Developing active and selective catalysts for crude oil cracking that fit into the current refinery system will go a long way in saving cost and time. In this review, catalyst formulations for the conversion of crude oil to light olefins have been discussed under the classifications: zeolite components, tuning of zeolite porosity, and matrix materials. USY has been the common zeolite that is used in the cracking of hydrocarbons to gasoline fractions, and ZSM-5 has the desired shape selectivity for cracking of paraffins in gasoline fractions to light olefins. At the same time, its low hydrogen transfer activity does not consume a large amount of generated light olefin, resulting in improvement of light olefin production. Various modifications of ZSM-5 composition have shown improvement in the light olefin yield. The wide range of hydrocarbons in crude oil makes pore size tuning of the zeolite especially important. Matrix materials generally increase the attrition resistance, hydrothermal and chemical stability, metal entrapment ability, coke resistivity, and fluidizable catalyst formation. However, they can also affect (positively or negatively) catalyst arrangement and active site properties, which makes careful selection very important.
The role of 3D alumina foam support (Al-F) and titania-modified alumina foam support (Al-F-Ti-X, where X represents the weight ratio of Al-F/TiO 2 ) on the dispersion and catalytic activity of NiMo metals in the hydrodesulfurization (HDS) reaction of dibenzothiophene was studied in a batch reactor. The catalysts were characterized by X-ray diffraction (XRD), N 2 adsorption desorption isotherm, field emission scanning electron microscopy (FESEM), Fourier-transform infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The Al-F and Al-F-Ti-10 dispersed the active metals better than the other supports, and more MoS 2 was formed on the Al-F-Ti-10 support. TiO 2 incorporation into Al-F decreased its surface area but also increased its surface acidity. The Al-F catalyst exhibited a relatively higher HDS activity (81% DBT conversion) over the conventional γ-Al 2 O 3 -supported NiMo catalyst (72% conversion). The modified Al-F-Ti-10 catalyst demonstrated the highest HDS activity of 97% DBT conversion after 4 h of reaction.
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