Elsevier

Catalysis Communications

Volume 46, 10 February 2014, Pages 86-89
Catalysis Communications

Short Communication
Proof of concept of the SCR of NOx in a real diesel engine exhaust using commercial diesel fuel and a full size Pt/beta zeolite/honeycomb monolith

https://doi.org/10.1016/j.catcom.2013.11.026Get rights and content

Highlights

  • SCR of NOx has been performed in a real diesel exhaust with commercial diesel fuel.

  • A full size Pt/beta zeolite/honeycomb monolith catalyst has been prepared and used.

  • The SCR behavior was similar to that reported for model hydrocarbons at laboratory.

  • NOx removal volcano-shape profiles, with maxima at 250 °C, were obtained.

  • The optimum THC concentration was 3000 ppm.

Abstract

The Selective Catalytic Reduction (SCR) of NOx has been performed in a real diesel exhaust stream with commercial diesel fuel by using a full size home-made Pt/beta zeolite/honeycomb prototype catalyst. Fuel was injected upstream of the catalyst to achieve total hydrocarbon concentrations between 1000 and 5000 ppm, and the SCR behavior observed was similar to that typically reported in laboratory experiments performed with model hydrocarbons. Typical NOx removal volcano-shape profiles, with maxima at 250 °C for all THC inlet concentrations, were obtained, with an optimum THC concentration of 3000 ppm.

Introduction

The main drawback of NOx removal on Diesel vehicles is the oxygen excess in the exhaust, and a reducing agent must be fed into the exhaust stream which must react with NOx in the presence of excess O2. Different reducing agents have been studied, most of them at laboratory scale, including H2, CO, different hydrocarbons, ammonia, urea, etc. [1], [2], [3], [4], [5], [6].

In the SCR (Selective Catalytic Reduction) technology [2], [3], the reducing agent is continuously fed into the gas stream and a selective catalyst is used to promote the reaction of the reducing gas with NOx with respect to the unproductive direct O2 combustion.

In the NSRC (NOx Storage and Reduction Catalyst) process [1], [2], [3], the NOx removal process is carried out in cycles of storage and reduction steps. During the storage steps, which occur in normal driving conditions, NOx is chemisorbed on a basic oxide present on the catalyst. During the reduction steps, the reducing gas is fed and reacts with the nitrogen compounds previously stored (and also with O2).

The SCR technology with urea or ammonia is commercially available for heavy-duty vehicles [6], and the NOx removal technologies suitable for cars are now in a step of optimization and improvement [7]. Some previous articles reported NOx removal studies in real diesel exhausts [2], [8], [9], [10], [11], [12], [13]. Copper and platinum titania based monolithic catalysts were tested for the reduction of NOx with hydrocarbons in real diesel conditions [10], [11], Ag/Al2O3 catalysts were tested for NOx reduction with ethanol in a real diesel exhaust [12] and Cu/titanium silicalite (TS-1) zeolite/cordierite honeycomb catalysts were studied for the simultaneous removal of the NOx, hydrocarbons and CO emitted by a stationary diesel engine [13].

From a practical point of view the most convenient reducing agent would be diesel fuel, because it is already on board on the vehicle and additional tanks and filling facilities would not be required.

In one of our previous studies, the SCR of NOx was successfully performed with propene in a real diesel gas stream (in a power bench) by using a Pt/Al2O3 catalyst [9]. Also, it has been demonstrated in laboratory experiments that Pt/zeolite catalysts outperform the behavior of Pt/Al2O3 due to the zeolites' ability of maintaining a high concentration of hydrocarbon in the catalyst [14]. In previous studies, Pt/beta zeolite/honeycomb monolith catalysts, with 1 cm diameter substrates, were prepared and tested in our laboratory for SCR of NOx with propene [15], [16].

The goal of the current study is to demonstrate that the SCR of NOx can be performed in a real diesel exhaust stream by commercial diesel fuel and using a full size Pt/beta zeolite/honeycomb monolith catalyst.

Section snippets

Catalyst preparation

A cordierite honeycomb monolith supplied by Corning was used as catalyst supports (14.4 cm diameter; 14 cm length; 400 cpsi).

Beta zeolite was loaded into the honeycomb monolith by dip-coating [17], [18], [19] with a water suspension of 9 wt.% commercial powder ammonia beta zeolite (Zeolyst International), 0.4 wt.% surfactant (Teepol) and 0.2 wt.% binder (a 40 wt.% suspension of colloidal silica in water; Ludox AS-40).

To obtain a homogeneously dispersed mixture, the slurry was stirred with a

Results and discussion

Fig. 2 compiles the catalytic test results obtained in SCR experiments. THC and CO removal increased with temperature (Fig. 2a and b, respectively) and NOx removal (Fig. 2c) followed a typical volcano-shape profile, with maxima at 250 °C for all THC inlet concentrations studied. The production of NO2 (data not shown for the sake of brevity) by catalytic oxidation of NO is low in all experiments, that is, the NO2 percentage with regard to total NOx is always lower than 10%. This behavior is

Conclusions

The results of this study demonstrated that the SCR of NOx can be performed in a real diesel exhaust stream with commercial diesel fuel by using a full size Pt/beta zeolite/honeycomb monolith catalyst.

The SCR behavior observed in the real exhaust with commercial diesel fuel was similar to that typically reported in laboratory experiments performed with model hydrocarbons. Typical NOx removal volcano-shape profiles, with maxima at 250 °C, were obtained, with an optimum THC concentration of 3000 

Acknowledgments

The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the Spanish Ministry of Science and Innovation (Project CIT-420000-2009-48), and EU for the FEDER resources.

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