An overview is given of the selective catalytic reduction of NOx by ammonia (NH3‐SCR) over metal‐exchanged zeolites. The review gives a comprehensive overview of NH3‐SCR chemistry, including undesired side‐reactions and aspects of the reaction mechanism over zeolites and the active sites involved. The review attempts to correlate catalyst activity and stability with the preparation method, the exchange metal, the exchange degree, and the zeolite topology. A comparison of Fe‐ZSM‐5 catalysts prepared by different methods and research groups shows that the preparation method is not a decisive factor in determining catalytic activity. It seems that decreased turnover frequency (TOF) is an oft‐neglected effect of increasing Fe content, and this oversight may have led to the mistaken conclusion that certain production methods produce highly active catalysts. The available data indicate that both isolated and bridged iron species participate in the NH3‐SCR reaction over Fe‐ZSM‐5, with isolated species being the ...

https://www.tandfonline.com/doi/pdf/10.1080/01614940802480122

The State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal‐Exchanged Zeolite Catalysts

Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals

Catalytic hydrogenation of nitrates has been studied since the beginning of the nineties. Despite the encouraging initial results the problematic of ammonium by-product formation is yet to be solved. This manuscript aims to be an overview of past and present research in the field and propose some key areas, which should be addressed to improve current and newly developed systems.

Catalytic nitrate removal from water, past, present and future perspectives

Heterogeneous acid catalysis by heteropoly acids (HPAs) has the potential of great economic rewards and green benefits. Its application, however, has been limited to some extent because of a relatively low thermal stability of HPAs, hence difficulty of catalyst regeneration (decoking). The aim of this paper is to discuss approaches to the problem of catalyst deactivation that could be instrumental to achieve sustainable performance of solid HPA catalysts. These approaches include: developing new HPA catalysts possessing high thermal stability, modification of HPA catalysts to enhance coke combustion, inhibition of coke formation on HPA catalysts during operation, reactions in supercritical fluids and cascade reactions using multifunctional HPA catalysis.

Heterogeneous acid catalysis by heteropoly acids: Approaches to catalyst deactivation

The effect of impregnation strategy on structural characters and CO2 methanation properties over MgO modified Ni/SiO2 catalysts

The transformation of acetone was carried out over a 04 wt% PtHMFI catalyst (SiAl = 60) under the following conditions: flow reactor, 160°C, pressures of acetone and hydrogen equal to 075 and 025 bar, respectively Methylisobutylketone, propane and traces of mesityloxide are observed as primary products while the other main products: 2-methylpentane and diisobutylketone result from secondary transformation of methylisobutylketone The reactivity of the reaction products and of probable intermediates: diacetone alcohol, isopropanol and propene was compared to that of acetone, which allows us to establish the complete scheme of acetone transformation Acetone is competitively transformed through bifunctional catalysis into methylisobutylketone and into propane The limiting step of methylisobutylketone formation is acetone aldolisation over the acid sites of the catalyst while that of propane formation is acetone hydrogenation over platinum sites Methylisobutylketone undergoes the same competitive bifunctional transformations leading to diisobutylketone (limiting step: acid coaldolisation of acetone and of methylisobutylketone) and to 2-methylpentane (limiting step: hydrogenation of methylisobutylketone)

Transformation of acetone over a 0.4PtHMFI(60) catalyst. Reaction scheme

Methyl isobutyl ketone (MIBK) was synthesized from acetone (Ac) and hydrogen over Pt-HZSM5 bifunctional catalysts. The reaction was carried out at 160°C, atmospheric pressure, and with a PH2/PAc molar ratio = 0.33, using a fixed bed and dynamic flow reactor. The results show that catalytic properties and coke formation largely depend on the ratio between the number of accessible hydro-dehydrogenation sites and the number of theoretical acidic sites (nPt/nA).

Effect of the metallic/acid site (nPt/nA) ratio on the transformation of acetone towards methyl isobutyl ketone

La presente investigacion indaga sobre la formacion que dicen los docentes universitarios poseer en cuanto al uso y dominio de las Tecnologias de Informacion y Comunicacion (TIC) para el apoyo de sus actividades academicas en el entorno educativo. Especificamente se abordo el tema, importancia de la formacion de los docentes en instituciones publicas y privadas. La investigacion es de tipo no experimental, descriptiva y de campo. Los resultados reflejan, en relacion a la formacion en TIC que dicen los docentes poseer para el uso y dominio en apoyo a las actividades academicas, es muy deficiente y en algunos casos nula.

Formación del docente universitario en el uso de tic. caso universidades públicas y privadas. (u. de carabobo y u. metropolitana).

Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure and acetone/H2 molar ratio=3 The reaction was carried out over Pt/HMFI bifunctional catalysts, with 030 wt% of platinum which was supported over three aluminosilicates (Si/Al ratio=40, 95 and 160) and a borosilicate (Si/B ratio=44) with similar dispersion The results show that catalytic properties depend greatly on density and strength of the acidic sites of the catalysts Moreover, the limiting step of the MIBK synthesis reaction (aldolization of two acetone molecules) is carried out over the acidic sites of the aluminosilicates, but not over those of the borosilicate, which considerably affects reaction selectivity

Acetone transformation into methyl isobutyl ketone over Pt/HMFI catalysts. IV. Effect of density and strength of the acidic sites

The transformation of acetophenone was carried out over a 0.5 wt.% Pd HFAU catalyst (Si/Al=17) under the following conditions: flow reactor, 250°C, pressure of ketone and hydrogen equal to 0.8 and 0.2 bar, respectively. The reaction products were identified either by comparison in GC with reference compounds: benzene (B), ethylbenzene (EB), styrene (EB=), cumene (IPB), isopropylbenzene (IPB=) and benzoic acid (BA) or through GC/MS coupling: 1,3-diphenylbutane (DPB), 1,3-diphenylbutenes (DPB=), 1,3-diphenylbutan-1-one (DPBO), 1,3-diphenylbut-2-ene-1-one (DPBO=) and 2,4-diphenyl-3-methylpentenes (DPMP=). These products are formed through three main reaction paths. DPBO= results from successive aldolisation of acetophenone and dehydration of the resulting alcohol over the protonic sites of the zeolite, DPBO from the hydrogenation of 1,3-diphenylbuten-1-one over the Pd sites (path 1). The formation of EB= involves hydrogenation of acetophenone followed by dehydration of the produced alcohol; EB results from EB= hydrogenation (path 2). DPB= can result from EB= dimerization (path 2) or from hydrogenation of DPBO followed by dehydration of the resulting alcohol (path 2). These reactions are similar to those observed during acetone and cyclohexanone transformation over bifunctional catalysts. In these reactions no alcohol intermediate is observed, which shows that alcohol dehydration is much faster than aldolisation and hydrogenation steps. The third reaction path which leads mainly to IPB, IPB= and BA, plays a significant role in acetophenone transformation whereas this path was very slow in acetone and cyclohexanone transformations. BA and IPB= result from acid cracking of DPBO=, IPB from hydrogenation of IPB=. IPB= undergoes also dimerization into DPMP= and IPB undergoes dealkylation into B over the protonic sites of the HFAU zeolite.

Luis Melo

Papers

Transformation of acetone over a 0.4PtHMFI(60) catalyst. Reaction scheme

Effect of the metallic/acid site (nPt/nA) ratio on the transformation of acetone towards methyl isobutyl ketone

Formación del docente universitario en el uso de tic. caso universidades públicas y privadas. (u. de carabobo y u. metropolitana).

Acetone transformation into methyl isobutyl ketone over Pt/HMFI catalysts. IV. Effect of density and strength of the acidic sites

Transformation of acetophenone over Pd HFAU catalysts—reaction scheme