Top PDF Converting homogeneous to heterogeneous catalysts

Converting homogeneous to heterogeneous catalysts

Converting homogeneous to heterogeneous catalysts

Homogeneous transition metal complex catalysts for organic industrial processes are converted to catalysts which are heterogeneous with respect to the reactants, and which have substantially equal catalytic activity to the homogeneous catalysts. This is done by reacting a normally homogeneous transition metal complex catalyst with a metal bridging ligand which substantially duplicates the ligand moiety of the metal complex, to provide a polymerized, normally solid, heterogeneous phase, transition metal complex catalyst.

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Advancement in the Utilization of Biomass Derived Heterogeneous  Catalysts in Biodiesel Production

Advancement in the Utilization of Biomass Derived Heterogeneous Catalysts in Biodiesel Production

Solid oxide catalysts derived from various renewable sources have produced significant yield of methyl esters of enhanced purity. These materials are sourced for due to their advantages ranging from low cost, recoverability and reusability, environmental benign-ness, thermal stability and high quality product generation. For a possible greener production process, many re- searchers in literature reported the use of biomass-derived heterogeneous cat- alyst in biodiesel synthesis producing high quality pure product. The catalysts were majorly modified through simple physical cost effective and energy sav- ing operations. This paper explores some of these bio-based heterogeneous catalyst used in biodiesel production via transesterification and esterification approach and their performance in FAME yield and conversion. The feeds- tock consideration which warrant the route selection, various approaches that are adopted in biodiesel production, performance of renewable heterogeneous catalyst and the measures that were adopted to enhance efficiency of the cata- lyst were considerably highlighted. It is observed that the prospects of organ- ic-based solid catalyst in biodiesel development is a promising enterprise compared to the conventional methods utilizing homogeneous chemical cata- lyst, which generates wastewater requiring treatment before disposal and ge- nerates product that may cause engine malfunction. This review work aimed at providing detailed and up-to-date record of the trend in renewable catalyst development in biodiesel synthesis. This is expected to inform a suitable selec- tion and reaction conditions in the development of biodiesel from the very many feed stocks.
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The development of magnetic granulometry for application to heterogeneous catalysts

The development of magnetic granulometry for application to heterogeneous catalysts

The final aspect of catalyst magnetic investigations that have received at- tention has been the application of the magnetic granulometry techniques. The re- versible, super-paramagnetic magnetic response has been modelled via the Langevin function described extensively for isolated nanoparticles, converting the average super-moment into an equivalent volume of metallic cobalt. Several preparations of Co catalysts have been demonstrated to possess the reversible magnetic behaviour indicative of the super-paramagnetic system 89;93;94;95 - focusing on particles in the range 3 - 6 nm. The majority of studies of this form for catalysts have focused primarily on the magnetisation vs applied magnetic field behaviour, avoiding the thermal fluctuations described by N´ eel. This is purely due to apparatus limitations as the magnetometry systems used for the study of catalytic systems are designed with redox (300 - 900 K) as opposed to cryogenic (2 - 300 K) temperatures in mind. Similarly, the majority of theses studies have been carried out by Chernavskii, us- ing a system with a maximum applied field of ≈ 7 kOe, significantly lower than the H M ax = 50 to 70 kOe systems generally available to the equivalent nanoparti-
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Fenton-Like Oxidation of 4−Chlorophenol: Homogeneous or Heterogeneous?

Fenton-Like Oxidation of 4−Chlorophenol: Homogeneous or Heterogeneous?

Heterogeneous Fenton-like catalysts have received considerable research attention because they could potentially be attractive for oxidative removal of organic contaminants from tertiary wastewater. However, process design is still hampered by insufficient understanding of the chemical pathways involved, and especially whether oxidation activity stems from heterogeneous surface chemistry or minute concentrations of dissolved metal ions in the homogeneous phase. Using inductively coupled plasma-optical emission spectroscopy (ICP-OES) in combination with pH monitoring and ultraviolet- visible spectroscopy (UV-Vis) we have monitored the degradation of 4-chlorophenol (4-CP) over two Fenton-like heterogeneous systems, namely FeO x supported on TiO 2 and CuFe 2 O 4 . We show
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Biodiesel production from microalgae by homogeneous and heterogeneous catalysis

Biodiesel production from microalgae by homogeneous and heterogeneous catalysis

Heterogeneous based catalysts were used with [Umdu et al., 2009] or without supports [Koberg et al., 2011a; Kouzu et al., 2008]. Among the solid alkali catalysts without supports, the most effective is strontium oxide (SrO) [Liu et al., 2007b; Koberg et al., 2011b]. For example, under mild conditions (< 65°C) and low SrO catalyst concentrations (under 3 wt% compared to oil), a biodiesel yield over 90% is obtained for a reaction time lower than 5 min with vegetable oils as substrates [Liu et al., 2007a; Koberg et al., 2011b]. Moreover, it has been shown that a SrO catalyst can be reused up to 4 times without any significant lost of performance during soybean oil transesterification [Koberg et al., 2011b]. Moreover, Koberg et al. [2011b] showed that SrO was slightly more effective than potassium hydroxide (KOH) to transform soybean triglycerides into biodiesel. Consequently, alkaline metal earth catalysts such as SrO could be effective to produce biodiesel from microalgae lipids with triglyceride conversions up to 100% [Koberg et al., 2011a]. Despite the fact that SrO is an effective catalyst, its reaction mechanism is still a matter of discussion. In fact, it has been stated by Liu et al. [2007a] that SrO was acting as a solid strong alkaline catalyst. On the other hand, it was recently argued by Koberg et al. [2011a] that a large part of the reaction was catalyzed by SrO while another part was catalyzed by Sr(OH) 2 .
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“Heterogenized Homogeneous Catalysts for Fine Chemicals Production: Materials and Processes”180-185

“Heterogenized Homogeneous Catalysts for Fine Chemicals Production: Materials and Processes”180-185

Raghunath V. Chaudhari is the Deane E. Ackers Distinguished Professor at the Department of Chemical and Petroleum Engineering, University of Kansas (KU), Lawrence, USA. He worked at the National Chemical Laboratory, Pune, India, for 30 years as Head, Homogeneous Catalysis Division before joining KU in 2007. His research experience covers interdisciplinary fi elds of homogeneous and heterogeneous catalysis, chemical reaction engineering and modelling of multiphase systems with current activities focused on biomass conversion processes and the design and development of novel catalytic materials. He has authored or co-authored a number of research papers, review articles and two books, the most recent one being on “Trickle Bed Reactors”, published in 2011 by Elsevier. He also teaches kinetics, reaction engineering and chemical engineering thermodynamics at graduate and undergraduate levels at KU.
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DESIGN AND DEVELOPMENT OF NOVEL HETEROGENEOUS NANOPALLADIUM CATALYSTS FOR ORGANIC TRANSFORMATIONS

DESIGN AND DEVELOPMENT OF NOVEL HETEROGENEOUS NANOPALLADIUM CATALYSTS FOR ORGANIC TRANSFORMATIONS

The immobilization and chemical modification of homogeneous catalysts to form heterogeneous analogues of well-defined structures anchored to an insoluble matrix is of current interest. If the catalyst is soluble under the reaction conditions, the separation of the catalyst from the reaction mixture becomes problematic. In a heterogeneous system, the catalyst can be easily separated from the reaction mixture by filtration. A high activity of a supported catalyst often calls for a large active surface area and, thus, for small particles, i.e. a high dispersion of the active phase. Because small particles, especially small metal particles, tend to sinter already at relatively low temperatures, these generally are applied onto a pre-existing support material which itself is thermally stable and maintains a high specific surface area up to high temperatures. In this regard we chose an ion-exchange technique to heterogenize PdCl 4 2- on various ion-exchangers such as layered doubled hydroxides
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Polymer Supported Ni(salen) Catalysts and Ni(II)-salen zeolite Y as Catalysts for Heterogeneous Electrohydrocyclization Reactions

Polymer Supported Ni(salen) Catalysts and Ni(II)-salen zeolite Y as Catalysts for Heterogeneous Electrohydrocyclization Reactions

Combining Ni-salen and zeolites has excellent literature precedent. [8] One example is the use of Co(salen) zeolite in a reaction in which phenylacetic acid was the major product from a mixture of benzyl chloride and carbon dioxide. [9] The homogeneous Co(salen) reaction and analogous heterogeneous Co(salen) zeolite reactions produced the same product with the same yield. However, the catalyst turnover was vastly improved with the Co(salen) zeolite catalyst. The efficiency of a catalyst is measured by its turnover, which is measured as moles of synthetic product per mole of Co-zeolite mediator. For the Co(salen) reaction, the ratio was 34, and for the Co(salen) zeolite reaction the ratio was 8 x 10 4 (or 2300 times the Co(salen) reaction). It was concluded that the improved catalyst turnover arose from the features of the zeolite framework. The frame of the zeolite allows a substrate to “dock” into the supercage of the zeolite and the reaction will occur inside a small confined space. In 2015, it was shown that Ni(salen) zeolite was used successfully in the electrooxidation of hydrazine. [10]
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Heterogeneous Catalysts for Biodiesel Production:             A Review

Heterogeneous Catalysts for Biodiesel Production: A Review

Abstract Biodiesel is a biofuel and appears on the world energy scene as a strong substitute for petroleum diesel for its renewable and less environmentally polluting character. It can be obtained from transesterification reaction of triacylglycerol from vegetable oils or animal fats with short chainalcohol in the presence of homogeneous or heterogeneous catalysts. In recent years the production of alkyl ester by using heterogeneous catalysts it has excelled due to their capacity for regeneration, reuse and reduction of processing stages. Several parameters have been evaluated in the reaction steps, such as amount of catalyst, molar ratio of alcohol:oil, temperature, agitation speed and reaction duration. Intrinsic properties of catalysts are also studied, such as porosity, surface area, catalytic activity and others. Therefore, this review presents the transesterification reaction of several raw materials, as sources of triacylglycerols, using short chain alcohols and different heterogeneous catalysts. Optimal conditions for each catalyst, as well as its respective reaction mechanisms, were summarized.
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17 th International Symposium on Relations between Homogeneous and Heterogeneous Catalysis

17 th International Symposium on Relations between Homogeneous and Heterogeneous Catalysis

ISHHC17 intends to offer a platform where scientists from academia as well as industry, can meet to discuss the recent advances in instrumentation, synthesis and molecular level reaction studies. The aim of ISHHC17 is to uncover and focus on common concepts that emerge from atomic, molecular and nanoscale studies of the structure, function and dynamics of the two types of catalysts.

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Transition metal complexes of triphosphorus macrocycles: A new class of homogeneous olefin polymerisation catalysts

Transition metal complexes of triphosphorus macrocycles: A new class of homogeneous olefin polymerisation catalysts

so far as they do not require a co-catalyst, and approximately one third of commercial poly(ethene) is made via the Phillips method. However, unlike the metallocenes, both the chromium- based catalysts are heterogeneous and therefore much less is known about the mechanism of these reactions and the nature of the active species is still uncertain. Theopold and co-workers 1d have investigated model systems that are homo-

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Esterification of Free Fatty Acid by Selected Homogeneous and Solid Acid Catalysts for Biodiesel Production

Esterification of Free Fatty Acid by Selected Homogeneous and Solid Acid Catalysts for Biodiesel Production

compared to ethanol for esterification reaction at 60°C (Pisarello et al., 2010). Methanol excess was used to shift the equilibrium of the reversible reaction toward the direction of ester formation according to Chatelier's principle (Feng et al., 2011). The molar ratio Methanol to FFA of 20:1 was set for all experiments, based on previous literature investigations (Jeromin et al., 1987; Robles-Medina et al., 2009; Koh, 2011; Santori et al., 2012; Coupard et al., 2014; Konwar et al., 2014; Fu et al., 2015). Acidified oil was first added to the reactor operating under batch mode, where the water circulating inside the jacket provided the heat necessary for the oil to reach the desired temperature. Then, the methanol/solid catalyst mixture was transferred into the reaction system. A mixing speed of 720rpm was set for the majority of experiments (Sendzikiene et al., 2004; Berrios et al., 2007; Pappu et al., 2013). In addition, several experiments were conducted at mixing speed fixed at 200 up to 900 rpm in order to study the mixing effect on overcoming mass transfer limitation. Reaction was continued for 90 min for most experiments, yet to study the effect of reaction time extended runs were performed for preselected duration in the range of 120-240 min, and intermittent samples were collected as reaction progressed for analysis. Initial experiments were repeated 4 times, and standard deviation was found to be within 4%. This indicated good reproducibility, therefore for subsequent experiments no replicates were conducted. The reaction temperature was retained at 60ºC that is below the boiling point of methanol (64.7 ºC) at atmospheric pressure (Sendzikiene et al., 2004) with the purpose of maintaining the methanol in liquid state without the necessity to pressurize the reaction vessel (Canakci and Gerpen, 2001). On the other hand, a set of experiments were performed at temperatures in the sequence of 30-60 ºC with the intent to investigate the temperature effect on the reaction system. The block flow diagram of the esterification reaction using heterogeneous catalyst is shown on Figure 4-7.
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Review on the application of modified iron oxides as heterogeneous catalysts in Fenton reaction

Review on the application of modified iron oxides as heterogeneous catalysts in Fenton reaction

2006). The Fenton reaction in which iron salts are used as catalyst is de fi ned as homogeneous Fenton process. In homogeneous Fenton oxidation systems, mass transfer limitations are negligible and the readily available iron ion in the reaction medium reacts effectively in the degradation process. However, there are some drawbacks encountered by this process that are mainly (i) pH-dependence of the system (2.5 e 4.0), (Katsumata et al., 2005) (ii) formation of ferric hydroxide sludge at pH values above 4.0 (Tamimi et al., 2008) and its removal issue (iii) the generated sludge may prevent UV radiation penetration in photo-Fenton process (Faust and Hoigne, 1990) which will affect treatment process (iv) dif fi culty in cata- lyst recovery (Pariente et al., 2008) and (v) the cost associated with acidi fi cation and subsequent neutralization that may limit the application of homogeneous Fenton oxidation system at industrial scale. Therefore, the application of heterogeneous Fenton reactions as a possible solution to overcome the shortcomings of homoge- neous catalysis has been put into perspectives by many researchers. This will enable pollutant mineralisation under non-controlled pH conditions and also for contaminated sites with pH adjustment limitations (Usman et al., 2012b). In heterogeneous catalysis, iron is stabilised within the interlayer space of the catalyst ’ s structure and can effectively produce hydroxyl radicals from oxidation of hydrogen peroxide, under non-controlled pH conditions and without iron hydroxide precipitation (Garrido-Ramírez et al., 2010). Several heterogeneous catalysts have been employed in Fenton reactions such as mesoporous materials (Chun et al., 2012; Xia et al., 2011), iron pillared clays (Chen et al., 2010), iron containing zeolites (Dükkanc ı et al., 2010; Hassan and Hameed, 2011) and iron min- erals (Lan et al., 2010; Magalhães et al., 2007; Ortiz de la Plata et al., 2010). There have been extensive studies on application of iron
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Single site heterogeneous catalysts

Single site heterogeneous catalysts

When certain kinds of organometallic, chiral catalysts are tethered to the inner walls of the mesoporous silica, it follows that the reactant’s (substrate) interaction with both the pore walls and the chiral directing group will be distinct from the interaction it would experience if the chiral catalysts were free (as in the case of a homogeneous catalyst). The confinement of the reactant within the mesopore will lead to a larger influence of the chiral directing group on the orientation of the substrate relative to the reactive catalytic centre when compared with the situation in solution. The validity of this strategic principle has been multiply attested in our laboratories [44,57] – see, for example, our work on allylic amination [60] (of cinnamyl acetate and
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Computationally Probing the Performance of Hybrid, Heterogeneous, and Homogeneous Iridium‐Based Catalysts for Water Oxidation

Computationally Probing the Performance of Hybrid, Heterogeneous, and Homogeneous Iridium‐Based Catalysts for Water Oxidation

Taken together, our results show that the intrinsic OER activity of the different model Ir-based catalysts via a WNA-2 mechanism increases as follows: Ir-hom ≈ Ir-hyb < Ir-het. With regards to the I2M mechanism, the comparison between the Ir-hom and Ir-hyb systems is more complicated due to the concurrence of electrochemical and chemical reaction steps. Nevertheless, the fact that Ir-hom requires a slightly lower overpotential compared to Ir-hyb (0.34 V versus 0.53 V), but a higher energy chemical step (0.59 eV versus 0.39 eV), indicates that these two catalysts might exhibit a comparable OER activity. The comparison of the overall activity between the three model Ir-based catalysts is also rather complex, as the lowest energy- demanding pathway for both Ir-hom and Ir-hyb is the I2M which involves a chemical step, whereas for Ir-het it is the WNA-2 mechanism. If we assume the same surmountable barrier for the chemical steps for Ir-hom and Ir-hyb, the activity trend is then dictated by the applied overpotential: Ir-het ≈ Ir-hom ≥ Ir-hyb. Although this trend is not conclusive, the high OER activity predicted for Ir-hom would support that this species might be part of the purple-blue solution, as suggested by Crabtree et al. [47] However, we note that the same authors also proposed
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HETEROGENEOUS CATALYSTS FOR ORGANIC TRANSFORMATIONS

HETEROGENEOUS CATALYSTS FOR ORGANIC TRANSFORMATIONS

This chapter describes the various catalyst/process options available for an industrial chemist to effect different organic transformations . It includes a brief introduction of homogeneous, heterogeneous catalytic systems and basic concept commonly encountered in catalysis such as selectivity, turnover number, atom economy etc. A brief discussion of polymer supported catalysts and the advantages in using polymer supported catalysts is discussed. A detailed discussion about cellulose is also described. The importance of selective organic transformations and the need for the design and development of environmentally cleaner catalytic methodologies is also highlighted. The origin of zeolites, properties of zeolites and their application in catalysis was described.
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Homogeneous and heterogeneous oligomerization reactions of olefins with unbridged metallocene catalysts

Homogeneous and heterogeneous oligomerization reactions of olefins with unbridged metallocene catalysts

The monomer 1-pentene was applied as a pure liquid. The activated catalysts were added at room temper- ature and after one hour reaction time, the products were identified by GC/MS. Table 1 describes the re- sults, and Figure 1 shows the GC of the products that are formed when complex 2/MAO was applied as catalyst.

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Activation of peroxymonosulfate by heterogeneous catalysts for the removal of organic pollutants in water

Activation of peroxymonosulfate by heterogeneous catalysts for the removal of organic pollutants in water

In previous study, most of the heterogeneous catalyst/PMS studies reported the efficiency of the catalyst but provide limited insights to the kinetics of the catalytic reaction. The investigations of the kinetics of pollutant oxidation in SR-AOP dealing with heterogeneous catalyst/PMS system are often based on the pseudo first−order kinetics with the assumption that the oxidant (PMS) added was readily available for reaction (Liu et al., 2015a; Zhang et al., 2013a). Qi et al. (2014) presented a second−order kinetic model to describe the degradation of caffeine by Co−MCM41 catalyst. However, these kinetic models did not take into account the influence of pH, PMS dosage and catalyst loading on pollutant degradation particularly under non−ideal conditions (e.g. non−excess PMS, different pHs, etc.). In this regard, a more robust, holistic kinetic model that takes into account these influencing parameters needs to be employed.
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Homogeneous to heterogeneous Face Recognition

Homogeneous to heterogeneous Face Recognition

Chapters 3 and 4 introduce probabilistic solution to the heterogeneous face recogni- tion problem. Probabilistic discriminant analysis (PLDA) is the first ever probabilistic approach in HFR research domain. It provides theoretical framework for applying concepts of probability in face recognition problem of different modalities. It pro- duces very good results on CASIA HFB and Biosecure databases comparing to the state-of-the art methods [75, 46, 81, 82, 83]. Probabilistic methods have far greater advantage over other statistical approaches e.g. careful modelling of noise , marginal- ization, coherent way of model comparison, deferment of final decision in case of big uncertainty etc. In proposed method, I manage to produce outstanding, comparable results merely using intensity features globally on VIS-NIR and Webcam-DigiCam databases. Experiments on PLDA have been carried out according to protocol setup of [107] which considers overlapping train and test sets.
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Heterogeneous catalysts for catalytic CO2 conversion into value-added chemicals

Heterogeneous catalysts for catalytic CO2 conversion into value-added chemicals

Single atom catalysts (SAC) represent atomically dis- persed metal catalysts on the surface of a support. They exhibit very distinct electronic structures and adsorption configurations of reactants and intermediates, with unique selectivity [207]. SACs have been used for elec- trochemical ORR [208, 209], HER [210], formic acid oxi- dation reaction (FAOR) [211], and CO 2 RR [212]. Ni

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