Selective catalytic reduction articles and systems

A selective catalytic reduction system comprising:

• a first selective catalytic reduction article comprising a first substrate including a first catalytic coating layer comprising a first copper-containing molecular sieve having a first amount of copper oxide;
• and
• a second selective catalytic reduction article comprising a second substrate including a second catalytic coating layer comprising a second copper-containing molecular sieve having a second amount of copper oxide that is greater than the first amount of copper oxide;
• wherein the first selective catalytic reduction article and the second selective catalytic reduction article are in fluid communication.