Laura B. Gutierrez

Synthesis and characterization of ZSM-5 coatings onto cordierite honeycomb supports

Zeolite ZSM-5 layers (up to ca. 30% by weight) have been synthesized on cordierite substrates, following either a direct hydrothermal synthesis procedure or a secondary growth method, in this case after seeding of the support. The Si/Al ratio in the synthesis gel ranged from 14 to 100, but layers with a high Al content (i.e. a low Si/Al ratio) could not be prepared directly on the cordierite support. However, MFI layers with a low Si/Al ratio were readily grown after depositing an intermediate Si-rich layer. The results also show that the Si/Al ratio of the synthesis gel has a direct effect on the morphology, crystallinity and orientation of the MFI layer formed.

Facile synthesis of SiO2–Au nanoshells in a three-stage microfluidic system

The capacity to produce nanostructured materials with well-defined, specific properties in relatively large quantities is crucial for the viability of emerging nanotechnologies. Core–shell plasmonic structures, such as SiO2–Au nanoshells, are a type of nanomaterial where the control of morphological properties is especially important, given the strong dependence of the plasmon frequency on their characteristic dimensions. Here we present a simple, robust and scalable process to exploit the advantages of microfluidics to manufacture these sophisticated nanostructures. We show that the main sequential steps required to obtain SiO2–Au nanoshells can be carried out in a simple microfluidic system with significant savings in time and effort, and with an improved control over the product properties, compared to a conventional batch processing operation.

EXAFS, TDPAC and TPR characterization of PtInFerrierite: The role of surface species in the SCR of NOx with CH4

Abstract Ferrierite exchanged with In and with Pt, In (InFerrierite and PtInFerrierite) is characterized by extended X-ray absorption fine structure (EXAFS), time differential perturbed angular correlation (TDPAC) and temperature-programmed reduction (TPR). The presence of different In and Pt species is correlated with activity and selectivity during the NO selective reduction (SCR) with CH4 in the presence of excess oxygen. Both catalysts are active and selective for the said reaction. When a dry feed is used, both monometallic and bimetallic catalysts behave similarly. However, when water is present in the feed, while InFerrierite loses activity in the whole temperature range, PtInFerrierite increases its activity at temperatures above 450°C. EXAFS characterization indicates that in PtInFerrierite only a fraction of Pt is at exchange positions, the remaining fractions adopting the form of PtO2 crystals located in the outer-surface of the zeolitic structure. When this bimetallic catalyst is treated under wet reaction conditions, the formation of small metal clusters due to the reduction of PtO2 crystals occurs. Thus, the increase in activity could be due to a catalytic effect of Pt metal clusters on the NO oxidation reaction (NO+1/2O2→NO2). TDPAC characterization indicates the presence of two In species both in the monometallic and in the bimetallic catalysts: In2O3 and (InO)+Z− (In at exchange positions), the latter being the active In species for the reaction under study. TPR results also suggest the presence of highly dispersed non-crystalline In oxide species not bonded to the zeolite matrix. Neither EXAFS results nor TDPAC characterization show the presence of intermetallic Pt–In species. The results of this work prove that EXAFS and TDPAC techniques, combined with TPR and activity measurements, are powerful tools for the characterization of bimetallic catalysts.

Perturbed Angular Correlation Characterization of Indium Species on In/H-ZSM5 in the Presence of Water and Catalytic Deactivation Studies During the SCR of NOx with Methane

An In(4 wt%)-impregnated H-ZSM5 catalyst was characterized under wet and dry conditions by time-differential perturbed angular correlation (PAC) and by temperature-programmed reduction (TPR). Different indium species were quantified, correlating their structure with the catalyst deactivation due to the presence of water during the NO selective catalytic reduction (SCR) with methane. The fresh sample contains ∼60% of indium oxide and 40% of (InO)+ species at exchange sites, the latter being the active species for the reaction under study. Under wet atmosphere, hyperfine interactions determined by PAC indicate the formation of two types of In hydroxide species and the decrease of both (InO)+ and In2O3. TPR and PAC characterizations also show that deactivation is due to the decrease of (InO)+ at exchange sites to form, after water is removed, different non-active In oxide species.

Characterization of the role of Pt on CoPt and InPt ferrierite activity and stability upon the SCR of NO with CH4

The selective catalytic reduction (SCR) of NO x with CH 4 in excess of oxygen was studied over a series of ferrierite-supported monometallic (Co, In or Pt) and bimetallic (Pt-Co or Pt-In) catalysts. Pt promoted the NO x to N 2 conversion of both Co and In ferrierite after the samples were reduced with H 2 at 350°C either under dry or wet reaction stream. The addition of 2% of water to the feed stream also increased the activity of the calcined PtlnFerrierite for the said reaction. Temperature Programmed Reduction and XPS results show the presence of Co ) , Pt ) , Co +2 , Pt +2 and In at exchange position in the samples with the highest activity and selectivity for the SCR of NO x .

CoPt clusters in NaMordenites as catalysts for SCR of NOx

A new material based on Pt and Co exchanged in NaMordenite for the selective catalytic reduction (SCR) of nitric oxide with methane in the presence of excess oxygen is studied. The incorporation of 0.5% weight of Pt and 2% weight of Co to the zeolitic matrix after calcination and reduction on H2 flow for 1 h yields a solid converting 100% of NO to N2 and, simultaneously, 100% of CH4 to CO2 with a CH4/NO ratio = 3 and 2% of oxygen in the feed at 450°C. When the oxygen concentration in the feed varies, the NO conversion goes through a maximum for 2% at 450°C. The incorporation of Pt also promotes Co reducibility; 1% is reduced to Coo in the monometallic sample and 13% in the bimetallic sample. XPS results reveal that in the calcined samples Co2+ is at exchange position and, after being reduced, there appear thinly dispersed Coo particles and exchanged Co2+ ions. A greater reducibility and a shift of the maxima in the temperature-programmed reduction profiles suggest a Pt-Co interaction. In order to get an efficient catalysts for nitric oxide abatement it is necessary that the highly dispersed Coo and Pto particles and the Co2+ and H+ ions at exchange positions be in intimate contact inside the mordenite channels.

High-Active Metallic-Activated Carbon Catalysts for Selective Hydrogenation

A series of low-loaded metallic-activated carbon catalysts were evaluated during the selective hydrogenation of a medium-chain alkyne under mild conditions. The catalysts and support were characterized by ICP, hydrogen chemisorption, Raman spectroscopy, temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR micro-ATR), transmission electronic microscopy (TEM), and X-ray photoelectronic spectroscopy (XPS). When studying the effect of the metallic phase, the catalysts were active and selective to the alkene synthesis. NiCl/C was the most active and selective catalytic system. Besides, when the precursor salt was evaluated, PdN/C was more active and selective than PdCl/C. Meanwhile, alkyne is present in the reaction media, and geometrical and electronic effects favor alkene desorption and so avoid their overhydrogenation to the alkane. Under mild conditions, nickel catalysts are considerably more active and selective than the Lindlar catalyst.