Catalysts do nothing for vehicle CO2 other than converting CO to CO2. Gas boilers will like ICE be with us for years to come. The government announcement was re new installation from 2023. But seeing the disruption and cost associated with ground source heat pumps I can only wonder how many houses can even physically accommodate such works. Air source heat pumps are an option but less efficient. The answer is a mix of techniques and fir older or more congested properties gas boilers running on a mix of gas/ hydrogen will reduce overall CO2, ( plus improved insulation) before translating eventually to all electric heating. We installed all electric in a house in Plymouth back in the mid 70s. It was great multi zones programmes and individual thermostats. But boy was it expensive back then.