Johnson Matthey DPF-CRT® and DPF-CCRT technology for diesel emissions

Johnson Matthey Continuously Regenerating Technology (CRT®) System reduces PM, CO and HCs from diesel emissions and utilises engine NOx to oxidise soot collected in the filter.

Johnson Matthey’s CRT technology integrates a diesel oxidation catalyst (DOC) with a diesel particulate (DPF) filter to remove PM from diesel exhaust while simultaneously oxidising CO and HC to CO2. The diesel oxidation catalyst converts part of the NO in the exhaust to NO2 which reacts with soot trapped in the filter preventing it from becoming plugged with soot. Combustion of soot with NO2 occurs at temperatures that are typical of most engine loads, eliminating the need for a supplemental heat source for diesel particulate filter regeneration. This is critical for systems in remote locations.

CRT system: Filtration, Oxidation and Passive Regen

  • Filtration of PM occurs in wall-flow filter
  • Oxidation reactions over the diesel oxidation catalyst:
    CO + ½ O2 + CO2
    HC + O2 + CO2 + H2O
    NO + ½ O2 + NO2
  • Regeneration of diesel particulate filter:
    2NO2 + C + 2NO + CO2


The CRT system is available in multiple configurations, including our low-profile systems for diesel emission control where space is tight. Built-in silencing is also an option. The CRT(+) is CARB (California Air Resources Board) verified for emergency and prime power diesel generators, and Johnson Matthey’s non-CARB verified DPF is the SDPF®. The CRT system greatly reduces diesel emissions containing PM, CO and VOC for cleaner energy and cleaner air.

Typical CRT System reduction efficiencies

Pollutant Reduction
PM > 85%
CO > 80%
VOC > 70%


Every CRT system is equipped with the CRTdm diagnostic module and data logger which provides extended data logging capabilities. The SOOT ALERTTM Monitor is an optional product that will alert the engine operator when regeneration of the diesel particulate filter is required.

Johnson Matthey first launched the CRT system in 1995 with CRT systems retrofitted to buses in Sweden. Since then, millions of CRT systems have been installed on on-road and off-road vehicles and equipment, as well as stationary engines which range in power from 40 kW to 4 MW. The development of the CRT technology earned the Johnson Matthey team the Royal Academy of Engineering MacRobert Award 2000, in recognition of an outstanding innovation to benefit society.

General enquiries

Joseph McCarney


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    Betty Ann Keen

    North America

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      DPF retrofit enquiries

      Our DPF team

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