Abdullah M. Aitani

Homogeneous catalytic reduction of CO2 with hydrosilanes

Catalytic CO2 hydrosilylation is a thermodynamically favored chemical process that could be potentially applied to large-scale transformations of this greenhouse gas. During the last decade, there have been an increasing number of experimental studies regarding metal-catalyzed CO2 hydrosilylation processes. The first examples of catalytic systems used for CO2 hydrosilylation employed late transition metals such as ruthenium and iridium. Presently, there are several examples of other catalysts, including transition metal species acting alone or together with B(C6F5)3, as well as metal-free frustrated Lewis pairs (FLPs) and organocatalysts which are able to perform this reaction.

Recent Advances in Reactions of Alkylbenzenes Over Novel Zeolites: The Effects of Zeolite Structure and Morphology

Alkylbenzenes form an important segment of petrochemical industry for the manufacture of widely used commodities and specialty products. Since the last review on this topic (8), numerous new zeolite-based catalysts have been synthesized, characterized and evaluated in various transformations of aromatic hydrocarbons. This comprehensive review covers major reactions of mono-, di-, and tri-alkylbenzenes such as disproportionation, alkylation, transalkylation, isomerization, etc., over different zeolite-based acid catalysts. During the last decade, significant progress was made in the synthesis and structure determination of novel zeolites, mesoporous single crystals, hierarchic zeolites and two-dimensional zeolites. These developments have enhanced the understanding of the role of zeolites (effects of structural type, morphology, acid sites, accessibility of acid sites, shape selectivity factors) in transformations of aromatics. In this review, the emphasis is on the influence of the type of acid sites, zeolite topology, and reaction conditions on the activity, selectivity and pathways of these reactions. Thermodynamics and reaction kinetics of transformations of aromatic hydrocarbons are also discussed. This article covers mostly literature published during the period of 2002–2013.

Characterization of Chromia/Alumina Catalysts by X-Ray Photoelectron Spectroscopy, Proton Induced X-Ray Emission and Thermogravimetric Analysis

Chromia/alumina catalysts with different metal loading were characterized using X-ray photoelectron spectroscopy (XPS), proton induced X-ray emission (PIXE) and thermogravimetric (TG) techniques to elucidate the surface structure of these catalysts. XPS studies on calcined samples show a sharp increase of the Cr/Al ratio at calcination temperatures up to 500°C while the ratio remains relatively unchanged at higher calcination temperature. The surface state of chromium shows predominantly Cr6+. At calcination temperatures higher than 500°C, calcination-induced reduction is observed of the Cr6+ to Cr3+, where the fraction of chromia in Cr3+ oxidation state increases with increasing temperature. A progressive increase of the intensity of the peak due to Cr 2p of the Cr3+ oxidation state is also observed with increasing amount of metal loading. The calcination-induced reduction of the alumina-supported chromia was found to be less than the corresponding reduction of bulk CrO3. Also, the size of the spin-orbit splitting of the Cr 2p level of chromia catalysts which had undergone calcination-induced reduction was found to be smaller than would be expected for bulk Cr3+. The XPS spectra of chromium on the Cr/Al catalysts were found to be time dependent. Photoreduction of Cr6+ on Cr/Al samples was found for irradiation times longer than 4.0 min. It was found from PIXE analysis that at higher calcination temperature, the Cr/Al atomic ratio approaches the values obtained by XPS. For all samples, the chromium particles were found to be homogeneously distributed on the alumina support for calcination temperatures up to 800°C. Thermogravimetric results on uncalcined bulk CrO3 agree well with the XPS observation as to the fact that the main phase transformation of Cr6+ compounds occurs at about 500°C, resulting in reduction to Cr3+.

Pathway to Ethylbenzene Formation in Side-Chain Alkylation of Toluene with Methanol Over Cesium Ion-Exchanged Zeolite X

To control the styrene to ethylbenzene ratio in the products of side-chain alkylation of toluene with methanol over Cs-X-based catalysts, pathway to ethylbenzene was examined. Styrene underwent transfer hydrogenation with methanol much faster than hydrogenation with hydrogen to ethylbenzene. Addition of Cs2O and ZrB2O5 to Cs-X enhanced and suppressed, respectively, the transfer hydrogenation.Graphical Abstract

FCC Gasoline Sulfur Reduction by Additives: A Review

Abstract This review covers publications in the open literature and patents issued during the last 10 years on issues related to fluid catalytic cracking (FCC) gasoline sulfur reduction. Emphasis was placed on FCC additives, their composition and performance. An attempt was made to elucidate the mechanism for sulfur reduction at FCC cracking conditions. Fluid catalytic cracking technology advances, both process and catalyst, have historically worked together to achieve significant improvements in FCC performance. There is every reason to expect that this will continue to be the case in the future. These advances will have an impact on the volume and quality of the FCC gasoline produced and will offer additional operating flexibility.

EFFECT OF ZSM-5 ADDITION ON PRODUCT DISTRIBUTION IN A HIGH SEVERITY FCC MODE

The high-severity fluid catalytic cracking (HS-FCC) process is a novel FCC process that enhances light olefins yield under high severity reaction conditions. The process has been investigated by using a small-scale FCC pilot plant (0.1 BPD) with a down-flow reactor. High severity reaction conditions are preferable for enhancing the production of light olefins by catalytic cracking of heavy oils. As another option for the light olefin production, adoption of ZSM-5 additive in conventional FCC units is well known. This presentation describes the effect of ZSM-5 additive on the catalytic cracking of vacuum gas oil under high severity reaction conditions, particularly focusing on the synergistic effect with the base catalyst. Three kinds of FCC catalysts with different activity were used as base catalysts. Although the employment of a ZSM-5 additive resulted in significant increase in the light olefins yield at the expense of gasoline in each catalyst system tested, the effectiveness was varied depending on the nature of the base catalysts. By choosing a suitable base cracking catalyst, more than 20 wt% of propylene yield was obtained at a one-pass conversion of fresh feed.

Environmental Benign Catalysis for Linear Alkylbenzene Synthesis: A Review

In this review, we discuss the recent advances in both of non-zeolitic and zeolitic solid acid catalysts for linear alkylbenzene (LAB) synthesis with special focus on improvements of 2-LAB isomer selectivity and catalyst stability. Effects of post treatment methods particularly dealumination and desilication on the catalytic performance of mordenite in terms of mesoporosity, diffusivity and deactivation mechanism are extensively reviewed. Perspective trends in the development of mesoporous zeolites for LAB synthesis are also presented.

Experimental determination of high-severity fluidized catalytic cracking (HS-FCC) deactivation constant

This paper presents the results of an investigation carried out to experimentally determine the deactivation constant of a fluid catalytic cracking (FCC) process. Kinetic modeling was performed using a four-lump model and an experimentally determined deactivation constant. Significant improvement was achieved in predicting the product gasoline, gas and coke yields compared to the yields predicted by models using a theoretical deactivation constant. Activation energies for each reaction are reported and compared with the literature values.

Chapter 1 Development of high-severity FCC process: an overview

Abstract High-severity fluid catalytic cracking (HS-FCC) is a new process for the conversion of heavy oils into lighter hydrocarbon products and petrochemical feedstocks. Research teams from Japan and Saudi Arabia are jointly developing this technology. The process combines mechanical modifications to conventional FCC with changes in process variables and catalyst formulations. The main operating regime of the process is a special down-flow reactor system, high reaction temperature, short contact time, and high catalyst/oil ratio. Experimental runs were conducted in a downer and riser-type pilot plants (capacity 0.1 BPD) and a demonstration plant (capacity 30BPD) using various catalysts, additives, and feed oils. Pilot plant results demonstrated the advantage of downer in suppressing back-mixing, thus increasing the yield of light olefins and reducing dry gas. Using paraffinic crude base vacuum gas oil (VGO), propylene yield of 25wt% was obtained under HS-FCC reaction conditions.

Thermal analysis of spent steam-reforming catalysts

Abstract Thermal analysis is a group of techniques in which changes in characteristic properties, of a physical or chemical nature within a substance, are measured as a function of temperature. In catalyst studies, thermal analysis may be used to obtain information on the thermal stability, composition, deactivation, activity and life of a catalyst. The method is especially useful for studying the transformations that occur in or on a catalyst when heated. These transformations include decomposition, phase transition, adsorption, absorption, desorption, dehydration, degradation and solid-state and gas-solid reactions. In this paper, the thermal analysis (TG and DTA) results of spent steam-reforming catalysts are presented. Ni/Al 2 O 3 catalysts, which had been in operation in a steam reformer for about 18 months, gave exothermic effects with corresponding weight gain in the temperature range 20–1130 °C. Ni/CaO/Al 2 O 3 catalysts, which had been in use for 30 months, however, gave endothermic and exothermic effects with weight loss between 20–850 ° C, and an exothermic effect with weight gain at about 900 ° C. These results and the significant changes observed in the properties of the catalyst along the reformer tube are discussed.