Jacob A. Moulijn

EVOLUTION OF NITROGEN FUNCTIONALITIES IN CARBONACEOUS MATERIALS DURING PYROLYSIS

X-ray photoelectron spectroscopy (XPS) was used to investigate the fate of nitrogen functional forms present in a lignite and its chars, chars derived from the model compounds acridine, carbazole and polyacrylonitrile (PAN). Four different peaks have been found in the XPS patterns, corresponding to at least five different nitrogen functional forms, all being aromatic moieties. The XPS patterns of the synthetic chars were recorded for identification purposes. The distribution of nitrogen functional forms changes with increasing severity of the pyrolysis conditions. Under mild pyrolysis conditions, firstly unstable functionalities like pyridones, protonated pyridinic-N and N-oxides of pyridinic-N are converted to pyridinic-N and secondly pyrrolic-N is converted to pyridinic-N during condensation of the carbon matrix. During the condensation process, nitrogen atoms are incorporated in the graphene layers replacing carbon atoms. After severe pyrolysis all nitrogen is eventually present in 6-membered rings located at the edges of the graphene layers as pyridinic-N or in the interior as quaternary-N. Upon exposure to the ambient, N-oxides of pyridinic-N can be formed. During pyrolysis, differences in nitrogen distribution of the char precursors have diminished. It is presumed that the remaining small differences in the nitrogen distribution of the chars cannot significantly influence the formation of nitrogen oxides during combustion of the chars.

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

Abstract Oil refinery related catalysis, particularly hydrodesulfurization (HDS) processes, is viewed as a mature technology and it is often stated that break-throughs are not to be expected. Although this could be a justified compliment to those who developed this area, at the same time it could also stifle potential new ideas. The applicability and perspectives of various desulfurization technologies are evaluated taking into account the requirements of the produced fuels. The progress achieved during recent years in catalysis-based HDS technologies (synthesis of improved catalysts, advanced reactor design, combination of distillation and HDS) and in ‘non-HDS’ processes of sulfur removal (alkylation, extraction, precipitation, oxidation, and adsorption) is illustrated through a number of examples. The discussed technologies of sulfur removal from the refinery streams lead to a wealth of research topics. Only an integrated approach (catalyst selection, reactor design, process configuration) will lead to novel, efficient desulfurization processes producing fuels with zero sulfur emissions.

Heterogeneous catalytic decomposition of nitrous oxide

An overview is given on the ongoing activities in the area of the decomposition of nitrous oxide, N2O, over solid catalysts. These catalysts include metals, pure and mixed oxides, supported as well as unsupported, and zeolitic systems. The review covers aspects of the reaction mechanism and kinetics, focusing on the role of surface oxygen, the inhibition by molecular oxygen, water and other species, poisoning phenomena and practical developments.

Structured Catalysts and Reactors

The present and the future of structured catalysts - an overview. Reactors with structured catalysts where no convective mass transfer over a cross section of the reactor occurs (monolithic catalysts = honeycomb catalysts): ceramic catalyst supports for casoline fuel metal and coated-metal catalysts autocatalysts - past, present and future monolithic catalysts for the selective reduction of NOx with NH3 from stationary monolith reactors unconventional utilization of monolithic

Science and technology of catalytic diesel particulate filters

During the last few decades, concerns have grown on the negative effects that diesel particulate matter has on health. Because of this, particulate emissions were subjected to restrictions and various emission-reduction technologies were developed. It is ironic that some of these technologies led to reductions in the legislated total particulate mass while neglecting the number of particles. Focusing on the mass is not necessarily correct, because it might well be that not the mass but the number of particles and the characteristics of them (size, composition) have a higher impact on health. To eliminate the threat of diesel particulate matter, essentially absolute filtration in combination with the oxidation of all emitted hydrocarbons is what will be required. After two decades of development, the first filters will soon be introduced on a large scale. Many different problems had to be overcome; it was especially important that the filter was robust and its regeneration was controllable. The key technology to controllable regeneration is oxidation catalysis, which is the main area of focus in this review. Catalytic filter regeneration is very complex, something which is apparent in the main aspects of catalysis (i.e., activity, stability, and selectivity). Complications are that the process conditions can be very transient and that the temperatures are usually low. It is shown that the oxidation catalyst cannot be examined isolated from the total system. Within the margins of size restrictions and an engines service life, essentially all particulate matter should be trapped, the filter should be regenerated safely, no toxic by-products should be formed, and the catalyst should not alter the filtration characteristics, and vice versa. The exhaust conditions of passenger cars are not favorable for continuous regeneration strategies, because the best strategy seems to be periodic regeneration with the aid of a catalyst. This concept is not passive, which makes it complex and expensive. The best technology for filter regeneration with trucks and buses seems to be continuous regeneration. Using the NO x present in the exhaust gas for soot oxidation amounts to a simple and robust concept. A future limitation might be the minimal required NO x :soot ratio; it is not sure if this will be met in future engines. Alternatively, a low-temperature catalyst may be developed that does not require NO x . Developing such an advanced catalytic trap will be one of the major challenges of catalytic filter engineering.

Catalyst deactivation: is it predictable?: What to do?

Abstract Catalyst deactivation is usually inevitable, although the rate at which it occurs varies greatly. This article discusses the causes of deactivation and the influence on reaction rate. Methods for minimising catalyst deactivation, by tailoring catalyst properties and/or process operations, are presented, as well as reactor configurations suitable for the regeneration of deactivated catalysts. Alkane dehydrogenation is used as an example to demonstrate the variety of engineering solutions possible.

Preparation of monolithic catalysts

Monolithic catalysts can be attractive replacements for conventional catalysts in randomly packed beds or slurry reactors. The conventional procedures for preparing catalysts, however, cannot simply be applied to monolithic catalysts. Different procedures are discussed on how to put a coat layer of a catalyst support material like alumina, silica, or carbon on a monolith body by either filling the pores in that support or by putting a layer on that support. Different methods to apply an active phase to the support are discussed as well. Finally, methods to convert ready-made catalysts into monolithic catalysts are presented.

Desilication: on the controlled generation of mesoporosity in MFI zeolites

Recent studies have shown that desilication by treatment in alkaline medium is, with respect to other methods, a very suitable and reproducible methodology to obtain mesoporous ZSM-5 zeolites with preserved structural integrity. This feature article analyzes mechanistic and kinetic aspects associated with this post-synthesis treatment. Framework aluminium controls the process of framework silicon extraction and makes desilication selective towards intracrystalline mesopore formation. An optimal molar Si/Al ratio in the range of 25–50 has been identified. At higher Si/Al ratios non-selective and excessive extraction of framework silicon occurs, while minor extraction and limited mesopore formation occurs at lower ratios. The presence of non-framework aluminium species, for example obtained by steam treatment, inhibits mesopore formation by alkaline treatment due to reinsertion of these species into the zeolite framework. Additional kinetic optimization of the physicochemical properties of the hierarchical porous zeolite structures is achieved by variation of time and temperature of the alkaline treatment. A successive combination of post-treatments, in which desilication is followed by dealumination, enables a decoupled modification of the mesoporous and acidic properties, being interesting in catalyst design and optimization. Preliminary work on other zeolite framework types has shown a promising outlook of the alkaline treatment. Development of mesoporous zeolites via desilication should induce a more efficient usage of the zeolite crystal due to an improved accessibility and a facilitated transport to and from the active sites.

Monoliths in Heterogeneous Catalysis

Abstract The use of structured catalysts in the chemical industry has been considered for years. Conventional fixed-bed reactors have some obvious disadvantages such as maldistributions of various kinds (including a nonuniform access of reactants to the catalytic surface), high pressure drop in the bed, etc. Structured catalysts are promising as far as elimination of these setbacks is concerned. Two basic kinds of structured catalysts can be distinguished: Structural packings covered with catalytically active material, similar in design to those used in distillation and absorption columns and/or static mixers. Good examples of catalysts of this kind are those offered by Sulzer, clearly developed by Sulzer column packings and static mixers. As in packed beds, there is an intensive radial convective mass transport over the entire cross-section of these packings. Structural packing catalysts and the reactors containing them are, however, not within the scope of this review. Monolithic catalysts are continuou...

Diesel particulate emission control

This paper reviews the emission control of particulates from diesel exhaust gases. The efficiency and exhaust emissions of diesel engines will be compared with those of otto engines (petrol engines). The formation of particulates (or “soot”), one of the main nuisances of diesel exhaust gases, will be briefly outlined. The effects of various emission components on human health and the environment will be described, and subsequently the emission standards for particulates and for NOx, which have been introduced worldwide, will be summarized. Possible measures for reducing exhaust emissions of particulates and NOx will be discussed, such as the use of alternative fuels, modifications to the engine and the use of aftertreatment devices. It will be made clear that aftertreatment devices may become necessary as diesel emission standards become more stringent, in spite of important progress in the other fields of reducing exhaust emissions. Selective catalytic reduction via hydrocarbons, ammonia or urea, a possible aftertreatment method for NOx emission control, will be discussed briefly. Filters for collecting particulates from diesel exhaust gases will be examined in more detail and aftertreatment control systems for particulate removal will be reviewed. These can be divided into (i) non-catalytic filter based systems which use burners and electric heaters to burn the soot once it has been collected on the filter; (ii) catalytic filter-based systems which consist of filters with a catalyst coating, or filters used in combination with catalytically active precursor compounds added to the diesel fuel; and (iii) catalytic non-filter-based systems in which gaseous hydrocarbons, carbon monoxide and part of the hydrocarbon fraction of the particulates are oxidized in the exhaust gases. Finally, recent trends in diesel particulate emission control will be discussed, indicating the growing importance of the catalytic solutions: the fast introduction of non-filter-based catalysts for diesel engines and the possible application of filters in combination with catalytically active precursor compounds added to diesel fuel.