sugg

Como nestes exemplos:

Unibanco - Investor Relations
In April, 2004, Mr. Moreira Salles was elected Chief Executive Officer of our Executive Board of Officers, continuing to serve as Vice Chairman of our Board ...
www.ri.unibanco.com.br/ing/hol/org/index.asp

ESCELSA - Espírito Santo Centrais Elétricas S.A.
Sole Paragraph - Upon resolution of the Board of Officers, the Company may open and/or close branches, agencies, offices and representative offices and any ...
www.escelsa.com.br/versao_ingles/investidores/empresa/Estat...

Translators have had problems with Diretoria because of the need to translate Conselho de Administracao as Board of Directors. The Diretoria is more "hands on" than a Board of Directors in the US is. I and a few distinguished colleagues have finally settled on this term and have seen it also simply as Executive Officers.

However it does seem a little odd in the specific context you have there. Usually on such a certificate you don't see Diretoria but Diretor, or Diretora. Or another title, referring to an individual, not a group.

So perhaps you could use just "Officers" of the .....