Diesel Catalysts Research Articles

Recovery of platinum from diesel catalysts by combined use of H2O2/HCl leaching and adsorption

Spent automotive catalysts are industrial non-hazardous wastes of high added values because of the presence of platinum group metals, whose recovery is gaining increasing attention in European countries. This paper proposes a hydrometallurgical process to recover platinum from diesel catalysts, based on a first leaching step with aqueous solutions of H2O2 (up to 0.2 M) and mild HCl concentrations (0.4 M), followed by a refining step in which platinum is deposited over a granular activated carbon. Tests were carried out at different H2O2 content, temperatures, and sizes of granulated catalyst. The use of H2O2 and low HCl content allows higher sustainability than conventional hydrometallurgical processes by reducing safety risks associated with the use of concentrated HCl and the emissions of NOx deriving from the use of nitrogen species in conventional leaching. Besides, the use of an adsorbent avoids the utilization of cyanides or other toxic organic solvents for the refining of the leaching solution. Experiments revealed that the low HCl concentration results in longer leaching times; however, process conditions can be tuned to completely recover platinum with negligible extraction of other metals on the catalyst, minimizing on the subsequent adsorption process. Optimal conditions appear as leaching at 20 °C with a 0.13 M H2O2 0.4 M HCl solution followed by an adsorption step at 20 °C using an activated carbon with high BET surface area and high content of reducing surface groups. These findings suggest that the proposed recovery process can be a suitable candidate for future technology implementations.

Electrochlorination as the basis for an efficient technique for extracting platinoids from spent diesel catalysts

Electrochlorination as the basis for an efficient technique for extracting platinoids from spent diesel catalysts

Effective Method for the Platinum Group Metals Extracting from Spent Diesel Autocatalysts

The team of authors described a solution to the problem of developing a fundamentally new technology for the industrial processing of spent diesel automotive catalysts containing platinum group metals (PGM) and SiC carrier, which has such advantages as carrying out a full processing cycle in one hardware module. The processing of SiC catalyst is extremely difficult by pyrometallurgical methods, but proposed technology is based on the electrochlorination method. The scientific novelty of the proposed method lies in the superposition of two independent electrolysis processes in direct and alternating, with varying frequency, currents under conditions of forced, continuous and complete recondensation of the electrolyte. The study of the diesel catalysts processing by the electrochlorination method have carried out.

Effect of structure and stability of active phase on catalytic performance of hydrotreating catalysts

For environmental protection and efficient utilization of oil resources, higher requirements for the selectivity, activity and stability of hydrotreating catalysts are proposed. To effectively solve this issue, the influence of structure and stability of active phase on catalytic performance of hydrotreating catalysts was reviewed. It was realized that the active phase structure essentially depends on the extent of metal-support interaction, and can be properly designed by adjusting catalyst preparation parameters (e.g. support properties and metal precursors in the impregnating solution) and sulfidation conditions (e.g. pressure, temperature and gas composition). As the hydrotreating conditions for gasoline, diesel and residue become severer, the active phase structures need much higher stability. The selectivity of gasoline hydrodesulfurization can be notably increased by selective post-treatment of the active phase structure. Well-dispersed active phase slabs with moderate metal-support interaction are needed for highly active and stable CoMo and NiMo diesel catalysts. New generation NiMo catalyst by strengthening metal-support interaction exhibits better residue hydrodesulfurization activity and stability.

The pH-dependent release of platinum group elements (PGEs) from gasoline and diesel fuel catalysts: Implication for weathering in soils

Powdered samples of new and old gasoline catalysts (Pt, Pd, Rh) and new and old diesel (Pt) catalysts were subjected to a pH-static leaching procedure (pH 2–9) coupled with thermodynamic modeling using PHREEQC-3 to verify the release and mobility of PGEs (platinum group elements). PGEs were released under acidic conditions, mostly exhibiting L-shaped leaching patterns: diesel old: 5.47, 0.005, 0.02; diesel new: 68.5, 0.23, 0.11; gasoline old: 0.1, 11.8, 4.79; gasoline new 2.6, 25.2, 35.9 in mg kg−1 for Pt, Pd and Rh, respectively. Only the new diesel catalyst had a strikingly different leaching pattern with elevated concentrations at pH 4, probably influenced by the dissolution of the catalyst carrier and washcoat. The pH-static experiment coupled with thermodynamic modeling was found to be an effective instrument for understanding the leaching behavior of PGEs under various environmental conditions, and indicated that charged Pt and Rh species may be adsorbed on the negatively charged surface of kaolinite or Mn oxides in the soil system, whereas uncharged Pd and Rh species may remain mobile in soil solutions.

Dissolution kinetics of Pd and Pt from automobile catalysts by naturally occurring complexing agents

Powder samples prepared from gasoline (Pt, Pd, Rh, new GN/old GO) and diesel (Pt, new DN/old DO) catalysts and recycled catalyst NIST 2556 were tested using kinetic leaching experiments following 1, 12, 24, 48, 168, 360, 720 and 1440-h interactions with solutions of 20 mM citric acid (CA), 20 mM Na 2P 4O 7 (NaPyr), 1 g L −1 NaCl (NaCl), a fulvic acid solution (FA–DOC 50 mg L −1) and 20 mM CA at pH 3, 4, 5, 6, 7, 8 and 9. The mobilisation of platinum group elements (PGEs) was fastest in solutions of CA and NaPyr. In the other interactions (NaCl, FA), the release of PGEs was probably followed by immobilisation processes, and the interactions were not found to correspond to the simple release of PGEs into solution. Because of their low concentrations, the individual complexing agents did not have any effect on the speciation of Pd and Pt in the extracts; both metals are present in solution as the complexes Me(OH) 2, Me(OH) +. Immobilisation can take place through the adsorption of the positively charged hydroxyl complexes or flocculation of fulvic acid, complexing the PGEs on the surface of the extracted catalysts. The calculated normalised bulk released NRi values are similar to the reaction rate highest in the solutions of CA and NaPyr.

X-Ray Absorption SpectroscopicStudies of Platinum Speciation in Fresh and Road Aged Light-Duty Diesel Vehicle Emission Control Catalysts

The species present in a variety of fresh and road aged light-duty diesel catalysts were determined by platinum L3 edge X-ray absorption spectroscopy (XAS). It was found that it is not sufficient to use the analysis of X-ray absorption near edge structure (XANES) alone to determine the nature of species present in fresh and road aged catalysts. Detailed analysis of the extended X-ray absorption fine structure (EXAFS) revealed the presence of a mixture of oxidic and metallic species in the fresh catalysts. Metallic components were predominantly found in the road aged catalysts. The present study did not find any chloroplatinate species in the systems investigated.

Platinum Group Metal Flows of Europe, Part II

SummaryA model of the use of the platinum group metals (PGMs) platinum, palladium, and rhodium in Europe has been developed and combined with a model of the environmental pressures related to PGM production. Compared to the base case presented in Part I of this pair of articles, potential changes in PGM production and use are quantified with regard to cumulative and yearly environmental impacts and PGM resource use, for the period 2005–2020. Reducing sulfur dioxide (SO2) emissions of PGM producer Norilsk Nickel could cut the cumulative SO2 emissions associated with the use of PGMs in Europe by 35%. Cleaner electricity generation in South Africa could reduce cumulative SO2 emissions by another 9%. Increasing the recycling rate of end‐of‐life catalytic converters to 70% in 2020 could save 15% of the cumulative primary PGM input into car catalysts and 10% of the SO2 emissions associated with PGM production. In 2020, PGM requirements and SO2 emissions would be, respectively, 40% and 22% lower than the base case.Substituting palladium for part of the platinum in diesel catalysts, coupled with a probable palladium price increase, could imply 15% more cumulative SO2 emissions if recycling rates do not increase.A future large‐scale introduction of fuel cell vehicles would require technological improvements to significantly reduce the PGM content of the fuel cell stack. The basic design of such vehicles greatly influences the vehicle power, a key parameter in determining the total PGM requirement.

Structural changes in air aged and poisoned diesel catalysts

Laboratory-scale ageing and poisoning procedures were performed on selected diesel catalysts. The results showed that phosphorus poisoning together with high temperature ageing has a strong effect on the catalytic activity and microstructure of platinum containing catalysts. Phosphorus poisoning contaminated the catalysts resulting in phosphate formation, e.g. CePO4 and AlPO4. Poisoning and air ageing increased platinum particle-size and washcoat grain-size.

Development of Efficient Zeolite-Containing Catalysts for Petroleum Refining and Petrochemistry

The role of various technologies in oil refining and petrochemistry changes due to amendments to the requirements for fuel quality. The development of these technologies requires the improvement of catalysts. This paper outlines main procedures for the production of dealuminated zeolites, as well as the advantages and drawbacks of these procedures. Catalysts with a high desulfurizing ability for the hydrocracking of vacuum gas-oil to gasoline and diesel fractions and catalysts for the isomerization of fuel hydrocarbons can be prepared using ultrastable Y-type zeolites. The results of testing of zeolite-containing binary catalytic systems in Fischer-Tropsch synthesis are presented.

Rare earth metals for automotive exhaust catalysts

The usage of rare earth metals for automotive exhaust catalysts is demonstrated in this paper. Rare earth metals have been widely used in automotive catalysts. In particular, three-way catalysts require the use of ceria compounds as oxygen storage materials, and lanthana as both a stabilizer of alumina and a promoter. The application for diesel catalysts is also illustrated. Effects of inclusion of rare earth metals in automotive catalysts are discussed.

Deactivation on Vehicle-Aged Diesel Oxidation Catalysts

This paper studies oxidation catalytic converters that were vehicle-aged in a diesel automobile. The deposition of several atoms (S, P, C, Si, Ca, Zn and Fe) was detected by several chemical analysis techniques. Moreover, AlPO4 and Al2(SO4)3 were identified by XRD. The catalytic performance of the aged catalysts with different mileages showed a similar degree of deactivation for CO and C3H6 oxidation. By contrast, laboratory sintering carried out on fresh catalysts revealed that it may have certain impact in the deactivation of diesel catalysts. Nevertheless, the possibility that the impact of chemical deposition on deactivation has a threshold value cannot be discarded.

Impact of ageing on the distribution of platinum group elements and catalyst poisoning elements in automobile catalysts

AbstractThe distribution of platinum group elements (PGEs) and catalyst poisoning elements (Pb, Zn, P and S) on the surface of gasoline and diesel automobile catalysts was investigated within this study. Laser ablation–inductively coupled plasma mass spectrometry (LA–ICPMS) provides both the sensitivity and the spatial resolution required for the surface analysis of sectioned automobile catalysts, and scanning along channels reveals the distribution of longitudinal changes in PGE and catalyst poisoning elements. Changes in catalyst surface features were studied for fresh catalysts and after ageing of the catalyst up to 80 000 km for both types of catalysts studied. The PGEs in the gasoline catalyst were found to decrease at the front of the catalyst after ageing, whereas the diesel catalyst presented a more constant loss along the catalyst. The fraction of poisoning elements (Pb, P and Zn for the gasoline catalyst and P and Zn for the diesel catalyst) retained by the catalyst is distributed non‐uniformly over the length of the catalyst. This could indicate different ageing mechanisms for gasoline and diesel catalysts. Copyright © 2003 John Wiley & Sons, Ltd.

Experimental and modeling study on zeolite catalysts for diesel engines

The work presented in this paper was aimed at detecting, understanding and modeling some critical behavior aspects of zeolite-containing diesel catalysts. An already available mathematical model for precious metal catalysts was used as a starting point. A specially designed set of experiments provided the information needed to improve certain modeling features. New submodels were introduced to account for hydrocarbon and H2O adsorption, as well as diffusion limitations in the zeolite. The effect of flow maldistribution during real world operation was investigated experimentally and computationally. Although a number of issues (especially regarding the DeNOx mechanisms) are not yet fully resolved, significant progress was achieved as regards the understanding and computational prediction of diesel catalyst operation.

Platinum-group elements: quantification in collected exhaust fumes and studies of catalyst surfaces

Automotive catalytic converters, in which Pt, Pd and Rh (platinum-group elements; PGEs) are the active components for eliminating several noxious components from exhaust fumes, have become the main source of environmental urban pollution by PGEs. This work reports on the catalyst morphology through changes in catalyst surface by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and laser-induced breakdown spectrometry (LIBS) from fresh to aged catalytic converters. The distribution of these elements in the fresh catalysts analysed (Pt–Pd–Rh gasoline catalyst) is not uniform and occurs mainly in a longitudinal direction. This heterogeneity seems to be greater for Pt and Pd. PGEs released by the catalysts, fresh and aged 30 000 km, were studied in parallel. Whole raw exhaust fumes from four catalysts of three different types were also examined. Two of these were gasoline catalysts (Pt–Pd–Rh and Pd–Rh) and the other two were diesel catalysts (Pt). Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing. The results show that at 0 km the samples collected first have the highest content of particulate PGEs and although the general tendency is for the release to decrease with increasing number of samples taken, exceptions are frequent. At 30 000 km the released PGEs in gasoline and diesel catalysts decreased significantly. For fresh gasoline catalysts the mean of the total amount released was approximately 100, 250 and 50 ng km −1 for Pt, Pd and Rh, respectively. In diesel catalysts the Pt release varied in the range 400–800 ng km −1. After ageing the catalysts up to 30 000 km, the gasoline catalysts released amounts of Pt between 6 and 8 ng km −1, Pd between 12 and 16 ng km −1 and Rh between 3 and 12 ng km −1. In diesel catalysts the Pt release varied in the range 108–150 ng km −1. The soluble portion of PGEs in the HNO 3 collector solution represented less than 5% of the total amount for fresh catalysts. For 30 000 km the total amount of soluble PGEs released was similar or slightly higher than for 0 km.

Effect of support oxide and noble metal precursor on the activity of automotive diesel catalysts

This paper reports on the investigation of the effect of noble metal precursor and support oxide on their catalytic activity for the conversion of diesel exhaust gas components. The noble metal precursors used in this investigation were hexachloroplatinic acid, platinum nitrate, and tetraammine platinum(II) hydroxide. As support metal oxides zirconia, a base metal doped alumina, alumina, and titania were used. Catalysts were prepared from all combinations of precursors and supports and were tested in an integral model gas test reactor both in the fresh and in the aged state. The catalysts were also characterized by various techniques including BET surface area, CO chemisorption, XRD, and TEM. The results indicate that the catalyst prepared from the tetraammine platinum(II) hydroxide precursor on the base metal doped alumina support shows the highest activity for the conversion of the gaseous exhaust components.